So i made a clone of my sim named "Ruby". And i put the clone in a throwaway 'hood. Basically, i wanted to swap Ruby and her clone's bodies because Ruby was a lookalike of one of my deleted sims who has the same name, but i realized i did mistakes. The Deleted Ruby had a lighter skin tone and her nostrils were not visible in normal view. I made the clone in BodyShop. Then when i swapped their GUID Numbers both Sims were corrupted; Their portrait was a red potatohead, their names are "Unknown" and their character file was inaccessible. This was astonishing because i tried this Method with Sims that had no character data and it worked, the clone's bodies were given to the OG Sims.

I can't access both Ruby and her clone's character file to even undo the change, what to do? Even worse, i couldn't bother to backup before the changes were done, and Ruby had relatives, and you should NEVER try to delete a sim with relatives normally (altho most of the time i didn't care because i would delete both relatives and the sim once i am done with a household)

Are you saying that the original sim in the original neighbourhood is corrupted, or the clone in the throwaway hood? There is a plugin called Alt Sim Surgery for SimPE with which you can clone a sim onto another safely.

Both of them are corrupted

If you don't have a safe backup, then I think you may have lost the sim(s) as you can't access the character file. Whether the neighbourhood is okay depends upon how bad the corruption is; if you can delete the broken sim in-game then it may be okay.

I'm not sure exactly why you were swapping the GUID of two sims in different hoods?

I wanted to place the sim in a throwaway hood.... but seems like the neighborhood isn't the only thing i'm gonna throw out