Not very much.
If you add 5 grams to the cartridge end and counterbalance this with 50 grams increae to the CW, the net increase in effective mass if 5.5 grams.
If you add 5 grams at the cartridge end and counterbalance this by moving a counterweight of say 100 grams back by 1/2 the existing distance the effective mass will increase by 6.25 grams.
Formulae supplied on request.
Mark Kelly