Domestic smoke detection and SPD requirements in line with BS7671 A2 2022

Hello,

I'd just like to ask for clarification relating to the requirements within BS7671 (specifically regulation 443.4.1 & definitions of a safety services in part 2) in relation to type 2 SPD provision for safety services.

We have a large stock of social housing where a rolling programme to upgrade Smoke and Carbon Monoxide detection within those properties is continually carried out. The current detection level is being upgraded to include additional detector/s from generally LD3 systems up to LD2 or LD1 (depending on FRA's to blocks), to the existing systems in line with the current recommendations of BS5839-6. 

The question is: Is there a requirement to install type 2 SPD provision to all these properties because of the additional detection being installed to an existing installation?

I can understand the installation of SPD's during a replacement CCU and/or a completely new smoke detection system, but having to install SPD's wholesale for just an addition to an existing smoke detection system, could be challenging in some cases.

Any assistance is appreciated.