50/50 on whether that is the correct thing to do, as PlusNet will probably try and use it and then find out that it does not work.
Put it this way, took a little while to get it confirmed in Openreach on the scenarios, and Thales had previously said they cannot create a MAC.
I'd be worried that if you give them a MAC, they'll migrate you to their ADSL2+ product with a subsequent upgrade to the FTTC service. PlusNet may opt for that route as a less 'dangerous' route and if minimal downtime is very important it may be a safer route.
As migrations from Digital Region are such a low volume situation if they go smoothly then I'll be pleased, but expecting issues.