D&D 5E Legendary monsters and Shape Change

[Nitrosaur]

Hello guys, I was talking with a friend about high level spells and came to the topic of Shape Change vs True Polymorph. We were reading both spells to see their pros and cons as a player, but then I got thinking about Shape Change for NPCs because of two sentences:

"You can't use any legendary actions or lair actions of the new form" and "You retain the benefit of any features from your class, race, or other source and can use them, provided that your new form is physically capable of doing so"

So, we know players can't use any legendary actions while shapechanged as they can't use any from the new form. But if a creature with legendary actions like a lich were to use Shape Change, could it use some of it's own original Legendary Actions while under the effects of the spell? For example, a lich shapechanges into an ancient white dragon and can't use the tail attack legendary action from the dragon, but could it use it's original cantrip legendary action?

 

[J.Quondam]

I'd think yes.
The spell notes, "You retain the benefit of any features from your class, race, or other source and can use them, provided that your new form is physically capable of doing so."
By my reading, that suggests that, so long as the new form has sufficient appendages, voice, or whatever to a particular legendary action with, the lich could certainly cast a legendary cantrip or whatever. A "legendary action" is just a "feature" off the lich's stat block, I'd think, so it qualifies for use while shapechanged.