If you reduce the tip weight by grinding it, the effective spine will be stiffer. Although they may fly very close to the same, the spine would not be exact on each arrow. In addition, each arrow starts out with variable spine within the group. So, although you can get weight to be very close to exact, matching spine can be very difficult - especially on some arrow brands. To match spine to even a somewhat close measurement, you'd have to pick arrows with very consistant spine on each side and them cut shafts until you had matching effective spines. I don't even know how this would be measured unless you devised a spine tester that had a movable end-support, so you could test each arrow with the ends resting on the supports.

If I had an arrow that measured .330 spine and another in the group that measured .340, the stiffer arrow is also likely to the heavier one. Cutting the heavier one, will make it even more stiff, resulting in even greater spine variation among the group. If you're shooting the whole group on the stiff side, then flight differences (with broadheads) might not be that great, but if spine is borderline, then fairly large variation in flight may occur.