change all your water walker dragons into hollies
No, not all. But maybe one or two?
A history that can be manipulated, changed or even wiped isn't worth much, is it?
True. You could allow changing of variant only for plants without offspring. And you could add variant changing to the history. Or only allow it for a week after the plant grew up.
only obtainable by breeding
What I really dislike at dragoncave is, that new people can't get the same as people who joined some years ago. I can never have a Frill, a Holly or simply a CB Shadow Walker. And I like them so much! If you can get old flowers only by breeding, it's the same. I don't care so much if a plant is bred or parentless, but for some people it's important. And if they want a parentless variant of everything, they should be able to get it.