Animating the Blend shapes should activate the wrinkles.
Is it expensive? Depends on your version of Unity.
Since Unity 2018 Blendshapes on skinned mesh renderers are dealt with on the GPU with Compute Shaders. But there's been some further optimizations since then.
Someone has done a performance test of 2019.4 and 2021.3:
https://gist.github.com/d4rkc0d3r/f77c1e96d4aeefd0d1eaf13fb096a2deFrom this:
- Each active (non-zero value) blend shape is a separate compute call.
- The more vertices changed in each Blend shape the longer it takes to compute.
- Empty blend shapes occupy no GPU memory.
- Unused but non-empty blend shapes do occupy GPU memory, but not compute time.
- Later versions of Unity (2021.3+) are better for performance.
- Versions before 2021.3 would have better Blend shape performance if the head mesh was separate from the body. (Assuming most or all of the body mesh is still present) But 2021.3 and above would not benefit from this.