You don't want to be cutting any tips during flowering. Those growing tips are your main top cola, let it come up through the screen just like all the other bud sites. This will still tend to be your largest bud, you don't want to be cutting it off at this point. If you're still in veg, with at least a week to go that's fine, but I don't do it. I fim some strains early on, others I just supercrop and shape them that way.