LP accrual limit - a better understanding

We set up our LP plans several years ago, so I'm a bit fuzzy on setting up something new, so this is a little rambling with lots of questions.  Currently, our PTO plan has a limit of 300 hours.  Employee can exceed the 300 hour balance until the first of a new year when we reset it back to 300.  We would like to change the plan to a limit of 300 hours at any time.  In other words, when the employee reaches the max of 300 hours balance, they will not accrue until the balance drops below 300.  Can you change an existing plan to accomodate this change, if so how?  If an employee's balance drops to 299.5, does the system allow them to accrue the .5 brining them back up the the max?  Also, is there a way to capture lost hours?  For example, an employee accrues 8 hrs each biweekly pay cycle.  In the example just mentioned, if .5 hours are added to the accrual balance to get to the 300 hour max, what happens to the remaining 7.5 hours?  Are they posted in anyway in Lawson.  I would appreciate some assistance please.