Hello mate, anybody correct me if I'm wrong but if you put a smaller front sprocket on the front to lower the gearing it messes up the the speedo to read faster than you are actually traveling so you would also need a speedo healer to correct it.
But if you enlarge the rear by 2 or 3 teeth which works out similar the 1 down on the front, you may have to extend the chain, unless you are putting on whole new set of chain & sprocket's then not so much of a problem.
I would favour making the rear sprocket bigger as the no healer needed, & also keeps the chain a good distance from the chain guides on the swing arm thus reducing wear there at bit.
Hope that was of some help and good luck on the Trials.