The problem with the standard roles/permissions lists supplied with PeopleTools is that they get overwritten during a PeopleTools upgrade. So it really isn’t wise to modify the supplied definitions. Clone them and give those to your users if you really must modify them. It might **seem** the quicker method to modify the supplied definitions but you will probably pay for it in the end 
Even if you don’t modify them always be aware that Oracle may add or remove permissions so a quick compare of the permissions after a PeopleTools upgrade/patch is well worth the effort.