Mod Dowloads

[DStocker429]

This is to anyone who can give me sound advice. I have been considering downloading a couple of new mods, both characters and locations. I'd like to know if anyone can give me the pros and cons of doing this. I read somewhere that if you add a mod to the game, it alters it. Is this true? I enjoy the game as it is played now and I don't want it to be changed in any way. I'd hate to have to uninstall everything, then run out and buy a new game because I screwed up the first one. Any help on this would be greatly appreciated.