They will only swap the ONT if there's some kind of damage to the ONT itself, but hypothetically speaking if the ONT and fibre is fine, then there's no need to swap the ONT. Changing of services on MFN is done logically.
No ONT swaps required for Calix ONT's with MFN, the only thing that needs to be made sure of is that the previous ISPs service has been removed so the new one can take effect.
Depends on the fibre provider, with this line being on Openserve's infrastructure. This shouldn't take too long as your B number is already set to go live by Openserve's systems. We need to give this up to 24 - 48 hours.