Any way to revert expression to default while viseme is active?

While making the viseme and expression blendshapes for my first avatar, I've run into some pretty severe warping issues while the viseme and an expression involving the mouth is active ingame. I didn't really foresee this and the method I've done for the mouth is kind-of a 2.5D flat cartoon mouth, so editing the blendshapes in and of themselves would cause issues across the board.

I was wondering if I could alleviate the problem via making the mouth blendshapes revert to its default stance while the viseme is active. Ideally the eyes would remain untouched, but if I have to separate the mouth from the rest of the face, that's entirely fine and would take no extra effort.

I'm extremely new to the VRchat creation scene (and Unity as a whole) so any help is majorly appreciated! Thanks!