I love your enthusiasm, but I have not tested that situation. I'm not sure what exact steps you are planning. Remember to backup your saves before doing something unusual, or at the very least save under a different name. Doing something rash with your sorceress could change her title, since she's a special NPC.

Edit: You can swap out for a magic sword or better staff, dependent on sim leveling up.

Let me know what you decide to do or have done. At any rate, I wish you luck.

I've been meddling with this for a time and it seems your instructions, Simmodder99, work well only with NPC characters. Trying it on actual heroes (the ones you have to create) will make the sky fall down and the world end. Seriously. All the oddities I experienced after modifying my heroes broke the game for me eventually.

But at least we know multiclassing is sort of possible. I hope someone will make a mod that makes the process safe and reliable.

Lol. What manner of events did you experience? Meteors? But, yeah, like I said in The Guide in #3 : Do not change your preexisting hero either.
Secondary minions and party companions are entertaining enough to play with for me. But hopefully we'll see where else we can take this in a mod...

I'm pretty sure that's not how the game's supposed to behave but I'm having too much fun.

The kingdom where my npc witch turned spy/wizard lives was a 4 heroes kingdom (king spy bard blacksmith), and she is now considered the fifth hero and local wizard, a viable option for quests needing one. The spy is not suffering from competition.
Her comportement didn't change the slightest, she's still sleeping in the king's bed rather than meditating in the middle of nowhere (an activity wizards in my other kingdoms enjoy way too much) and still spends most of the day inside the castle.
(Didn't notice autonomous spy actions)
She's just somewhat legitimately playable.

(Tasks requiring her to "go back to the tower" are validated with hill walking because there's nothing up there)

Waiting for the game to break any minute from now !

Hmm... I've got to try the witch scenario then. Sounds fun.

In my case, I foolishly started with modifying my main heroes. Results were rather satisfying untill I finished a quest or exited to kingdom mode. Then the game suddenly forgot what hero I was playing with and froze on me. So - the world ends in a timeless abyss.

There were also other quirks, like wizards forgetting most spells with a sword equipped. But that was already described in the thread, I believe.

On the other hand, it all works with NPCs. If only a character isn't assigned to a building as a hero, the game is suddenly very lenient.

Aha! I think I just discovered a way to relatively safely multiclass one of your main heroes. It's really simple. So simple, I feel stupid not to think of it earlier.

1. Take one of your heroes, except Monarch or either one of the Priests (start a quest).
2. Shift-left click on him, when you have testingcheats enabled. Add him a profession of your choice.
3. Then - repeat the step above, but adding your original profession this time (if you were a Wizard turned Spy, turn Wizard again).

This guarantees the game will remember your hero, he stays assigned to the proper building, can cast all spells he should be able to cast, can do the right responsibilities, etc., etc. In one word - the hero remains playable.

At the same time, most of the abilities from the second profession remains with him. There is a risk, however, that professional activities that can be failed will not trigger correctly - like, for example, pickopocketing (my wizard-spy-wizard has such option in the dialogs, can perform the animations but earns no gold on success). Also, all the abilities triggered on objects will likely not trigger. For example, my wizard-bard-wizard can play lute, gather inspiration, etc., but he can't write poems and plays on the archive.

Reloading the game, however, doesn't cause any additional issues. It seems that TSM remembers your choice of professions and uses the last one you set as the default.

So, happy multiclassing everyone.

Yep Apepis, this works a charm! I did that with one of my Hero sims (think it was the Physician) and was able to keep him - I started him off as the Physician, changed him to Wizard, then changed back to Physician. He stayed in the Clinic, recognised it as home, had some Wizard spells, was able to cast them, was abe to scry too I believe, but did all his Doctoring too . So all went well - so far.... my game has decided to die on me, so am in the process of re-installing it - but I'll definitely be doing this when I get back into it. It's a loada fun, ain't it? Lol... Thanks for posting up your finds for the rest of us

hello excuse my English because I do not speak English so I speak from google translation but I have a problem I got to Step 5 and I shift + left click and myself: not available interraction
can you help me please

Is your game in french by any chance ?

yes it changes anything?

Eh bien, apparemment quelques "mods" ne marchent pas avec a version française du jeu... j'ai lu quelque chose là dessus dans la section "Mods"

I have the Spanish version of the game and it's working fine, though I must say I installed it in English.

ok it's not too serious then I'll do without

Opening Post instructions fully updated as: Dark Wizard's Guide: How to Multi-class Sims

thank you for the tutorial I will try with the mods TheHologramMan's and combine your tutorial is perfect

Seems to me ALL these hacks and mods have always had some kind of bug ever since Sim Original. Some work, some don't and some work most of the time and some work some of the time and some work only if this or that and guess what, sometimes when it worked before, it doesn't work now, or vice versa. So when control geeks start arguing in a forum it really turns me off. Especially when one of them insists that nothing can ever go wrong and gets angry at the person suggesting something could go wrong. Anyway, I will try this method as with all other hacks and mods with a fully backed up installation of the game (not just a saved game). I don't need to be told once, let alone twice, to beware the possibilities of something messing up, and someone angrily assuring people nothing can go wrong doesn't stop me from believing something can, indeed.

I've been multi-classing for ages, lol, using Dynamic Professions mod, and the only trouble I've ever had is with my Jacoban Priest having the spies abilities. I did not add the Spy profession to him, but simply added the SCOUNDREL ability of the spy using the Dynamic Professions mod. My Jacoban Priest when attempting to question a Pirate/Guildsman in the Questioning Chair receives no acceptance that the respo had been accomplished, so he will end up having shirked his responsibility, UNLESS....(this is my workaround for this problem and it works)...If this responsibility shows up for your Priest with Scoundrel ability, then simply type disablerespos in the command prompt, wait for them to turn off and a green check mark appears in the respos boxes, then type enablerespos in the command to get the responsibilities started anew, and most likely the Priest will have a fresh set of respos different from Questioning a Pirate or Guildsman. You can now also remove the abilities you have given to a hero sim, using TZ Dynamics Profession mod now, so one might also choose to remove the ability at the time of the respo to Interrogate, or Persuade, then re-add the ability back after the respo has been completed using TZDynamicsProfession mod latest version.
I would have liked to have seen this thread ages ago, though, so I could have known there would be conflicts with the Priest's as Simmodder suggested. LOL
My monarch, Xylan Darksword, is also a Wizard, and as mentioned with the Priest above, I added only all the abilities of a wizard to him, but not the profession of a wizard, and he is the best of wizards, but also he never had the respos of the wizard, he only gets kingly respos, but when he fights the beast in the Pit of Judgement, he uses his staff, and not the sword, even though both are equipped in inventory. In fact he is a better wizard than my wizard. By the way, he can also find the object Arcane Edge needed to make the 10 wizards staff in the forest or on the sea. He also has the abilities of a blacksmith, so he can make his staffs, armor, and swords earlier in my game than have to wait for my blacksmith Qyall Quartz to level up. Below is a pic of Xylan Darksword casting a spell in the Town Square: