Add something to the SDK to select the blendshapes to use for selfie expression (Like we can for the visemes and blinking) , or add a parameter in the Built-in Parameters for selfie expression.

Using the webcam in VRChat is a really cool feature and a cheap way for people use their avatars more expressively, but currently there's little to no documentation about what blendshapes are being used.

You also can't use a custom blink animation if you want to have the option to use selfie expression since it's trying to use the blendshape specified in the avatar descriptor.