that is an acceptable form of pruning for vals. In fact it may even spur more vigorous growth (as typically pruning does). Just trim the leaves as close to the crown as possiible with a clean cut, so you don't damage the plant. If you don't get very close to the crown, you will have an unnatural look to the pruned areas, which can ruin the effect unless hidden behind some decor. I learned this technique on larger swordplants. I originally didn't prune close enough, and the "nubs" took a while to die off, so the plants looked kinda unnatural for a while after pruning.
Also, with vals, I've just snipped off the ends (even tried rounding the ends off a bit. They would grow so quickly that this was an easier way to do things as they reached the surface. The ends continued to look very natural, and the plant seemed unnaffected in it's rapid growth. I'd suggest trying both methods and seek which one works best for you.
