How to clean up almost-symmetrical vertices? I'm working with a low poly game model, and I need to fix some vertices that are symmetric by design, but somehow were made imperceptibly asymmetric by rounding error or something.

I need to fix that asymmetry so I can use tools like Select Mirror and so I have the ability to mirror shape keys.

The mesh has some intentionally asymmetric aspects in texture mapping and geometry, so I can't just delete half the model and apply a mirror modifier. Also the model is rigged and I don't want to lose the bone weights.

Is there a way to broadly fix the asymmetric vertex positions in a vertex selection?

The only way I've found to fix it by hand only works with one vertex pair at a time:


Select both vertices
Hit s Shift+x 0 Enter to eliminate Y+Z variation.
Set the median X coordinate to 0 in the Transform Properties


This works for single vertices, but I need to clean up 562 such verts, so doing it one at a time is out of the question.
'Snap to Symmetry' under Mesh in Edit mode should do it.

https://docs.blender.org/manual/de/dev/modeling/meshes/editing/basics/symmetry.html

'Symmetrize' on the same menu may also help, but note that it is quite destructive.