It all depends on type of compressors.
By adding shims, the bumping clearance reduces in tandem type compressors.
It also depends on where you add the shim.
in normal reciprocating types, if you add shims at con rod the bearing clearance will increase nothing will affect the bump clearance.
In tandem types, adding shims will reduce bump clearance – shims are added at the bottom of piston rod of tandem type.
The other method is using gaskets on the cylinder head of varying thickness