Suspect it'll be set up for low(ish) pressure 300 - 350 psi so screwing a changer in in place of the reg probably won't work (well, not without serious valve work), nothing to stop you screwing a changer into the bottom line though (technically you should replace the macroline with steel hose if you're doing this). Research on regged pump cockers seems to suggest about 35 shots from 12 grams so this should get simular.