Mesh_Tools_Modifiers_Apply_Subsurf - Diffeomorphic/import_daz GitHub Wiki
Apply Subsurf

Modifiers are normally applied with the Apply button in the modifer context. However, this does not work if the mesh has shapekeys. The Apply Subsurf button does apply the subsurface modifier, even if the mesh has shapekeys. The shapekeys are also subdvided.
Apply Multires
The Apply Multires tool works like the Apply Subsurf tool, except that it applies a multires modifier instead.
Apply Active Modifier
The Apply Active Modifier tool works like the Apply Subsurf tool, except that it applies the active modifier instead.