I've no idea how you could overwrite any enchantments, I was poking at it just this morning and the existing one's don't seem clickable. Maybe it only works with that specific "Disappointer" rifle, which might be worth testing.
I finished up the White March and additional 3.0 content (there is a continuation to the big 2.5 update quest that leads to the definitive "hardest fight" in the game, whoo-boy) and I just adored the second part of the White March and it's ultimate conclusion. I really like the next content, from spells and abilities to the new soul bound weapons (and armor!) though the process of unlocking soul bound items (some of them, at least) continues to be my least favorite mechanic. It's not terrible, just kind of annoying for about a quarter of the items. They tend to be really powerful, so I suppose it makes sense.
I may well keep going with my third party just because I feel like I want to keep playing!