So long as you know how to "cycle the database" then you can play away till your heart desires and clear anything you like afterwards. When you want to clear your inputs go into DATA page 1 and then line select 4L which will take you to the status page. Flip the databases over by selecting the lower case "old" database as then active BUT please remember for the next crew to put it back as they might not catch it during their preflight.
I think you will have to manually delete any waypoints that you might create separately but that is on the same page at 5R.
FCOM pro-nor-srp p01-10 refers. It's under FMGS Initialisation.