There are inventory editors that let you store items out of game, copy them, and extract relics and charms. But as far as I know, unfortunately, an editor for individual items has never been made for Titan Quest. Everything I ever saw suggested that, while not necessarily impossible, it was extraordinarily difficult to do because of the way that Titan Quest handles item stats.
I've seen some suggestions that it would still be attempted, most recently from the creator of the TQDefiler who goes by SoulSeekkor. Even that, though, was some months back at least. I know he's still active online but there hasn't seemed to be any updates on recent progress so I'm not sure if he's still working on it or not. I too would love to see an item editor happen, but I'm not holding my breath for it, lol.
There is some sort of item editor. I was playing online and was given a sword that doed over 5 million damage, has unrealistic stats and so ona nd so forth. Cool things, hell I use it...and is funny as hell to watch things blow up!