Can an employer distinguish vacation hours accrued from prior ownership for final paycheck?

Our company has implemented a "use it or lose it" policy but to help employees with high balances they are allowing a one time carryover and some vacation payouts. However, with one employee (on admin level) due to the highest balances, they arranged to make 5 payout scheduled once a year over the next 5 years. But to protect themselves, can the employer make an agreement with this employee that should he leave the company the final vacation payout out (as per state law) will only be from current company accrued vacation time and will not include any vaca hours accrued from prior ownership? But should he remain with the company he will cont to have access to all his vacation time and will receive his vacation payouts that are scheduled.