Mentioned to Tess, that I had seen something along the lines of a scroll that could be used to exchange one legndary weapon trait for another.

Just had a quick look and can confirm these do exist, however are for the guardian class only (which is where I must have seen them):

Guardian overpower legacy exchange scrolls

Basically Overpower is now a forced 2h stance for all intents and purposes. Problem is a lot of 1h had Overpower legacies on them. To fix this problem, they can buy a scroll that will replace the Overpower legacy and replace it with a Pool A 1h legacy.

Available from guardian trainers (21st hall)