I've also been really frustrated when I've accidentally converted by rarity instead of category. My suggestion would be to have a slider like you see in the Options window on the Out of Set conversion side.
Can we try enforcing the Name Release Policy? Characters level 1-5 would be flagged as inactive after 30 days and characters level 6-20 would be flagged as inactive after 90 days. As of March 2nd there were 1,207,409 characters of which 330,397 have logged in in 2020. March 30th is the 90th day of this year. There's a large number of names that could potentially be released.