I've got an E46 M3 spoiler on my E36. It was installed by a body shop last spring after I had just polished, AIO'd, and SG'd the car, so I don't think the prep was ideal. Anyway, it has been slowly detatching from on of the ends. I can live with it now, but it's gonna need to be redone.

Can the 3M tape be easily removed from the bottom of the spoiler and replaced? Any tips? I assume I can use the floss trick to remove it from the trunk.

Well, I do not know how well it comes off, but I do know that it works well. It is far better than any other option regardless. I doubt it would be too hard to take off and shouldn't damage the paint at all. I used it on my M5 lip and it's been on for almost a year and a half with no problems at all.
Seth