Ok guys I'm new to hacking brawl so go easy on me

The first question is whats the difference between pac and pcs ?
I somewhere read that pac is the moveset but isn't that a psa file ?
Then I wanted to know if it is possible to load stages/stage textures while the game is running.
As in adding new maps ? I know replacing is possible but can't I just replace a "custom map" (made in the editor) with a new stage from here ?