Simple suggestion, let us "lock" attachments so that they aren't removed when we switch avatars (e.g when we drag a folder of attachments onto ourselves), unless there is a replacement.
What do I mean?
I have a HUD attachment I'd like to keep all the time, but it gets removed when I switch to another avatar. I would like to "lock" it so that it stays on me unless the new avatar has something that attaches to the same attachment point. So if I dragged on an avatar with a different HUD attachment in the same place, then it would remove my "locked" one, otherwise the locked attachment will stay.
This would however work for all things, like festive Christmas Mistletoe and the likes.
This is handy because it means if I have any no-copy attachments, then I can still use them to create different outfits or characters. E.g a no-copy mech with a hat, but I can also switch to a fox with a hat, without needing to buy two copies of the hat, or switch it about myself.
Mainly the concern is HUD attachments though, they're a nice feature but having to re-add them annoys me =)