If the Project Manager is saying I specifically want this, let's say Brand X toilet roll, rather than any other brand, you should invite hime to change the Works Information or Scope to be more specific. That would be a change to the WI / Scope which is a compensation event.
In the NEC3 ECC, consumables provided by the Contractor for the PM and Supervisor are a Defined Cost under 43(i) of the full Schedule of Cost Components and 53(h) under NEC4. So under a target cost contract, which by talking about "share amount" I assume you are under, this adjusts the Prices. i.e. the changes in the Prices = change in Defined Cost from using Brand X toilet roll versus what you were supplying at the moment.
Under options A & B of NEC3, the relevant clause of the Shorter SCC is 44, while under NEC4 it is 53(h).
Glad we've got to the bottom, so to speak, with who pays for toilet roll.