If your building has been fitted with a fully compliant 8629/BAFE SP207 evacuation system what are you to do come month 13 post commissioning, clearly the standard requires a mandatory service provision which should be done by the installer/commissioning incumbent – IF you choose to change the incumbent then this really should only be to one of those on the BAFE SP207 register.
That said, a change of contractor even under the scheme terms should also require a full system takeover test including a full acoustic test for the sounders in the flats so full access would need to be agreed before this was signed off.
It would not be considered acceptable for you to, for example, to pass the service provision for your evacuation system to someone not on the 207 register, as such a contractor would not be able to demonstrate competence.
Evacuation systems should, in accordance with the “golden thread” of connectivity and the new Gateway processes now covering projects of this type ONLY be undertaken by contractors with proven and accountable competence and SP207 certified.