Hi, and welcome HighBeta.
No idea about requesting an MSAN change, maybe some of the other wisened bods may be able to help.
The reason I'm posting, is to make you aware of the FTTC roll-out. Not every Cabinet (PCP) will get Fibre initially. The decision as to what Cabinets will get Fibre will be down to the Fibre Planners. Rumour has it that a lot of sway will be given to the out-lying Cabinets where current speeds are relativeley poor. I think thats quite fair TBH.
Even if your Cabinet
is chosen as part of Phase 1 FTTC. There will only be availability for the first 100 EU's who show an interest in taking up BT Infinity.
I've never accessed it, but I was told by my Fibre Trainer that there is a BT Infinity website where you can apparently vote on getting your Cabinet upgraded (or something like that). If you get other 'locals' fed off the same cabinet, ask them to vote as well. I would imagine it's something the Planners also take into account when coming to a decision.