The MAC would be fine, the name is irrelevant.
You say you are "staying there". First, is your mum happy for the line rental to be moved to an 18-month minimum term with PlusNet? Have you fully considered the things that are included by BT but chargeable at PlusNet? There's more to phone charges and hidden extras than the rental.
Second - have you thought about what happens if and when you decide to migrate the broadband elsewhere or cease it at your mum's because you have moved out? As I understand it, these days - contrary to what a PlusNet rep said here several years ago, the PlusNet line rental would have to end as well and the line be transferred elsewhere.
My broadband basic info/help site - www.robertos.me.uk
| Domains,website and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync ~ 53.4/16.8Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.