I want to add townie pools that I've found online to my uberhoods but I don't want a random empty subhood to be attached to my uberhood. Should I use some mod to invite every townie from the townie subhood to an actual liveable hood and make them playable and then again a townie? What would be the best way to transfer these townies from a townie pool subhood to other subhoods? After I'm done with that I can just delete the empty subhood they came in?

If the sub neighborhood where the townies are located is empty, with no sim living in any lot, you can delete it without problem. Townies will continue visiting your main neighborhood. Deleting sub-neighborhoods is safe as long as there are no Sims living on any lot.

Amazing! Thank you very much for letting me know

1. Add the townie pool subhood to the intended neighborhood.
2. Delete the subhood from the neighborhood.

The sims added by the townie subhood will remain as townies. No need to move them all onto a lot in another subhood!

Also, to add on to what Sokisims said - it's fine to delete subhoods with sims currently living there/occupied lots. The game will evict anyone who lives there and you'll find them in the family bin. Just make sure to move any gravestones before deleting the subhood. If you forget, the graves will get deleted. You can still get the graves back afterwards but you'll need to use a mod to respawn them.

It's just for the empty townie pool subhoods but good to know. Thank you for your quick assistance!

I had never deleted a sub neighborhood with sims living in it, I didn't know that! ^^ It's useful to know!!