Yes and no. No official thing yet (scenarios might provide something like that, but they’re kinda wobbly at the moment), but I’ve made something that allows you to just do that. Relatively easy, too.
Technically, Jelly only supports replacing trees and other fauna right now (which does, of course, not stop you from simply pretending that rocks are just another type of flower) but I could easily add options to have your own stuff generated independently of the current fauna at your own density/spread rules.
If you fancy a look, the documentation for said jelly feature is over here.. It’s documented much more complicated than it really is though, flowers are relatively easy for example