FrogReaver
As long as i get to be the frog
It sounds like that will work.
It's not overpowered because he can only do it once per turn. The rest of the time (Reaction, Extra Attack, whatever) will be normal Weapon damage.
Although (for style and flair) the Rogue may not appreciate a holy strobe light embedded in his blade
The charismatic rogue might rather like that...