As Lemontea said, the information pertaining to your character(s) is stored on the server. This means that there is no local \"save file\" for your character. Client settings are stored locally on your computer though, so things like your shortcut buttons and key mappings will have to be copied or recreated if you wish to have them on another client installation.
Open source means that the source code of the game is available for anyone to use(within the limit of the license model used).
The artwork like maps, textures, music and so on is under a more restrictive license to prevent people from using it directly or to create derivative artwork of it. If you did use it, Atomic Blue might have grounds to hold you in violation of the license agreement and take legal action against you.
What you could do, is to make your own artwork, but use the PS code in your own games.
So, there is no way for normal players to change the stats or skills of their characters beyond training it in game. There may of course be some bug that can be exploited to give a player unfair advantages, but it would not be acceptable, so the Devs(Developers, the people making the game) and GMs(Game Masters, the in game moderators of the game) do what they can to stop this. Please do report bugs and exploits, so that they can be handled with. Also, if you suspect a player is cheating, they are abusive, or in violation of the
Ingame Rules of Conduct, you may report this to a GM or submit a petition about it.