You can try to change the vlan size by changing the subnet mask, if you are not using the next or previous network. But if you have the option to move the AP to another vlan, as you mentioned, why dont put the APs on that vlan alltogether?
Button line, this is not a good way to handle an important infrastruture like Wi-Fi. Changing lease time, deleting leases on server. Apply a solution by increasing vlan size or assigning a new vlan for that mater. Best way to move forwad and not worry about it anymore.