NSO to ISO - Vesting Question

We have a client with an optionee that was initially brought on as a consultant.  He was granted an NSO at that time with a vesting start date that aligned with his true start date.  He has since transitioned into a full-time W2 employee.  The Board now wants to cancel the existing NSO and grant a new 'replacement' ISO with the same vesting schedule and vesting start date.  Are there any issues with this?   He has continued service since he started, no interruptions.  He understands that the grant date would change (and the clock would start on the ISO holding period  based on that new grant date)