lara,
trying to adjust a pellet by cutting it won't give you any idea about what your actually shooting, since the pellets are 50 grain equivalents, and not really 50 grains by volume. Check your pellets on a weight scale, and you will see the terrible difference in them. Loose powder is the only way to make adjustments in the loads that will be accurate.
If you want to play with pellets you can by pellets in the 30 grain loads and add one with a 50 grain pellet, to get 80 grains, and so forth.