Is modding a video game legal?

It depends on the game. You would have to check the liscense agreement. Many games allow you to, like The Sims 2.

Unless you have permission from the game's copyright holder, it's technically probably a violation of copyright. You'd have to have a compelling "fair use" exception to the copyright protection for...

Emulators are legal, as they are just software, as long as you don't have a ROM, it's perfectly legal to download a Emulator.

If it is the authority would have to sueue alot of people because youtube is crawling with gameplay vids. sorry but i dont know the solid answer :-(

If you mean like fire burn I don't think it matters if it is yours. But if you mean like copy burn than I think it is illegal. It is legal to make a backup copy of a game you purchased. It is...