Quick questions about mods

Hi, i just have a few questions.

Can a mod have two setup-modname.tp2 in its files?
What's the difference between tp2 and tpa ?
Some mods have their tp2 outside of modname folder, generally the folder isn't even named folder. Is it safe to rename the folder and move the tp2 inside? If no, can some find/replace magic solve that?

Thanks.