Using out-of-the-box GP, the answer is yes. A Purchase Order is not really an 'accounting event', so nothing you can do with a Purchase Order transaction in GP has any impact on the General Ledger. If you were to say the PO is received and create a Receipt or Invoice transaction - that would have GL implications, but nothing on the PO itself.
All of that said...there are a thousands of third party products and customizations out there for GP. If you are running anything that's not standard GP, this question gets exponentially harder to answer without more detail. So the best approach would be to test this - hopefully you have a test company set up where you can do that? If not, then before you do anything you're not 100% sure of, get all the users out and make a backup. :-)
