I have all heroes and most every one is blessed. the few who are not i'm holding off to see what happens.
A good way to do this I suggest is give us 1 token that we can exchange at the enchanter for each blessing we own. That way it's a one time thing.
This gives plenty of time for people to test and see best in slot for each hero.
THis also protects players who play multiple games and are away but will be back in a month or two. Or even players who come back over time so they don't get here realize all their hard work is gone if whatever exchange you come up with is over before they get back.
If they make future changes to the Blessings above the patch when changes happen tokens should again be issued each time regardless of how minor the change. Why? that minor change may seem minor to them but affect our hero in a way that makes some other blessing better. It's just the right thing to do not taking away all the game loyal time we put into it.