Woah. It is extremely expensive though so it would be pointless even if you could edit an eternal but an edited eternal is extremely powerful, especially on pets, maybe a limit of no eternal pet crafting with this "angel crystal".
Then there's the issue of cheaters but then again, they could already edit pets and eternals.
Another issue is crystal stash limitation but that's about it. 50 obsidian is a bit expensive just to edit an eternal for one build and those obsidians ain't easy . Then again, 50 obsidian can be quick to get given few days of farming but the barrier between people who spend hours and people who spend less time becomes more extreme as well.