You have to be completely sure, that you know, what you're doing, else you could easily invalidate your save file that way. You could edit other things like character voice and even some events, but that's a lot trickier. Now for the 'editor', there's Dragon Age Toolset, you can edit everything with it, from stats of your whole party, each character individually, to gold, to approval, to inventory capacity. You can edit your choices, but you can't upload that World State back to Origins, can you? It matters for later games, mostly for Inquisition, from what I've gathered.
Dragon Age Keep isn't ideal for what you want.
