Yes go ahead. Start on the inside and work you way out. Prune all branches that branch into the center and one of the double branches going in the same direction. Remember don't prune too severly because you'll have to see it all year.

Here is a link that might be useful: Propagating Perennials

Sap starts rising rather early in maples so don't be surprised if you see some bleeding. Not to worry - it's more of a concern to the pruner than it is to the prunee :-)) And use a very light hand. Japanese maples seldom require much in the way of pruning except to remove any obviously dead wood, occluded branches or to lightly thin the canopy and enhance the natural form. Nothing looks worse than an overpruned JM and they take a long time to outgrow it.

You don't want prune any tree when they are putting out there flush growth, the reason for this is that a tree is putting out lots of energy at that time bleeding doesn't hurt a tree

How can I tell if my japanese maple is no longer dormant?
Also what is "flush growth".

It is hard to tell exactly but generally when bud swell starts it's breaking ...it is very likely a bit before but unless you are a fortune teller you won't know til the swell ...as far as flush growth ...no it has nothing to do with a toilet ;>) it is during spring early heavy growth peiod and sometimes ltr in the summer a fall flush also happens but not with every cultivar and not every season in my experience ...but many have both. Late fall flush along with early fall freeze is not good for man, beast or Jm's...it won't kill a healthy tree but you will have dieback on all flush branches...that is why late summer and fall fertilizing is NOT recommended for JM's especially in colder climates .David