Plenty of mons do change abilities routinely.
Seadra for some inexplicable reason loses Swift Swim for Poison point before reverting back to Swift Swim for Kingdra.
"Baby" abilities like Pick up and Run Away often get exchanged for stronger abilities, though none of that applies here.
In any case there's sufficient precedent, and I really like Leaf Guard. One think that might be interesting if we want to change both abilities for Embirch would be Reckless, which would be the opposite kind of shift towards Rock Head rather than previous Pokemon that shifted away from it.
[17:53] <&Deck_Knight> If I Cite and Prune CiteandPrune's post, what does that make me?
[17:54] <Birkal> a citeandprune cite and prunner
[17:54] <%DHR> O_o lol
[17:54] <+Mos_Quitoxe> Cite and Prune doesn't do enough of either
[17:55] <+Mos_Quitoxe> can we make him change it or force him to pay damages
[17:55] <&Deck_Knight> It would be a lot easier for him to Cite and Prune if we made him a mod.
[17:56] <&Deck_Knight> I delegate this task to Birkal.
[17:57] <Birkal> >:|