In the "update rx" screen, am I allowed to change the "quantity dispensed" field to a value that makes the current fill a 90 day supply?

Lets say the customer is picking up his prescription and wants a 90 day supply instead. Also, lets say the current fill he is picking up for this prescription at the moment is a 30 day supply, and he has 2 refills remaining. Put together, he has enough quantity for a 90 day supply. He wants to pick up a 90 day supply right now. Can i go into "update rx" and change the quantity dispensed to another quantity to make it a 90 day supply instead of 30? Is it as simple as that or do we need to create a 90 day exception, call his doctor, etc?