HaloMods "Classic" Read-only Archive

I've made Halo trainers using TMK, but I want to do it with VB instead. How would I go about doing this? I have the offsets, I just need it to find that offset within a game's memory and replace what's there. Any help would be appreciated. and I'm not an idiot when it comes to VB, I've just never edited memory with it.

Edit: I'd settle for just knowing how to edit a file that isn't in memory, for example, finding an offset within a tag and replacing what's there