However, shutting off the heating basically means closing the pool. Will tenants in the building be able to claim rent reductions for the duration, due to reduced facilities?
Maybe, but that’s for the landlord to deal with. Including their input to decisions of the OC.
And can the committee and/or owners corporation do this anyway without a by-law since it is altering common property?
What’s being altered? In reality, OCs restrict access to common property all the time.
As long as they don’t block 24/7 access across common property to the lots and do it fairly there’s usually not a problem.