if you mean by making the thickness of the injection kit vernier thinner than the one provided by Bandai then the only way that I know is putting it on the low speed electric drill and scrapping out the inside... Yea I know this sounds silly but that's the only way that I know and also seen few modellers doing...
Other than that you will need to get those metal vernier kits to replace...
there are several different version on the market or will be on the market..
Met*lSku*k carries those and will also carry some of replacement resin parts for MG kits from Korean modellers...
people living in glass colonies shouldn't throw nuclear stones.