If you mean for Torchlight 1, then:
Game is saved in this path: %userprofile%\Application Data\runic games\torchlight
Just back up the shared stash file, do your thing, replace the file and reenter game. You need to be in title screen where replacing the file, not in game, otherwise it won't work. Take from the SHARED stash in your inventory the items you want duplicates of, go to main title screen, overwrite file of shared stash from the backed up one (in which those items you withdrew were still inside shared stash) and there you go! Upon entering game they are going to be in your inventory and shared stash, all at the same time!
If it is about 2, sorry, i haven't got it yet.
Post edited June 27, 2016 by KiNgBrAdLeY7