Allow redefine of standard DHCP options
Currently, it isn't possible to redefine any standard DHCP option that is defined in Kea. This is a good practice because it prevents administrators from shooting themselves in the foot. However, DHCPv4 is quite old and there have been some newer RFCs that define options that vendors previously could freely use.
An example of this is an older vendor of IP phones who used option 156 with some of their equipment. Option 156 is part of Bulk Lease Query now (RFC 6926) since about 2013. This IP phone manufacturer existed from 1998, however. This option was not defined in ISC DHCP, and so could be used there. The option is defined in Kea, though not presently used. Option 156, in the RFC, is defined as containing an integer as a flag of sorts. The old IP phone vendor needs option 156 to contain a string of some kind. This is only an example. This is probably not a one-off situation.
It is unreasonable to require administrators to purchase new equipment as part of the move to Kea, and therefore, it would be better to, in some way, allow the redefine of standard options. This should probably be a deliberate act somehow, perhaps requiring a keyword of some sort, so that the administrator is aware of what they are doing.