Here is a link to a campaign mod tool:
{Release} Mass Effect 3 SE[Mod Tool] - xpgamesaves
I have used it myself, and it works great. You might have some issues with the game loading it, and it'll put you back at an older save, just pause, click load, and pick the save you modded. It'll say it's corrupt, and ask if you want to delete it, just hit no and load anyway.