ReMeshing two vertex groups to different resolutions Some modifiers allow me to select a vertex group upon which to operate.

The remesh modifier doesn't.

I've got a 3-D mesh of a head, and I need the ears remeshed to a very high resolution and the rest of the head to a much lower resolution.

I have created 2 vertex groups.  Now I could {save, remesh, export to .OBJ} for each group, then create a blank project and import both .OBJs.

Assuming the re-meshing process has not messed up the join-perimeter, they should still fit together.

Is this the best way to do this?

EDIT: I've just realised that the perimeter will be messed up.   Say you have a cylinder with 100 points around the circle.   Cut it in half, now you have two cylinders.  Reduce one of them so it has 10 points around the circle. Now obviously these are not going to match up.  So is there some way to 'glue' them back together?
you could always seperate the mesh (select the ear in edit mode, hit P and seperate based on selection) then remesh each object individually, apply the modifier, and then join (and manually stitch or use bridge if possible)