You are thinking of doing exactly what I did do.
Initially I just switched my line from BT Retail to Pulse8, then set about thinking whether to stay with PN for my FTTC, move that also to Pulse8, or possibly go for AAISP Home::1 (76/20, 100GB). In the end I plumped for AAISP, though have not ruled out moving back to Plusnet. My reason for leaving them was concern over the new support systems and the never-ending problems some people were having with speeds. That was before anything was known about their upgrading of their backhaul which I think is still in progress.
There was no problem at all - I simply filled in the online form, then the couple of editable PDFs that came back re the order confirmation details and T & Cs etc. All very efficient and smooth. No problem with keeping my number, as it remains on WLR3 with just a different message on 1571. If I moved the FTTC to them then I believe it would become LLU'ed.
Note that the £13 includes basic 1571 but does not include caller display. I opted for that so am paying £14pm.
I also contacted Plusnet re not closing my account completely when I left, but moving me to an email-only one. That allowed me to keep receiving referral payments from them. Only relevant if you do receive referral credits at the moment, or use their email system, which I don't.
(Edit - you have Pluse8 in the subject and contents. It's Pulse8, or more precisely Pulse8broadband).
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 59546/15321kbps @ 600m. - BQM
Edited by RobertoS (Sun 10-Apr-16 14:46:14)