What I don't want, is an FTTP install at the rear of the property where the existing line comes in, but that is the only route available for anything Openreach-based, as that's where the poles are.
Some years ago, when BT tried mid-contract price rises, I left BT without penalty so it is possible if they want to make changes that you do not agree to: Therefore, if you do want to leave; I would not agree to a change to EE or another part of BT as that would certainly mean a new contract period.
It seems that you had already planned to move to VM, (in November), mainly because they will install the service to the front of your property, (via old underground ducts), and you do not want any Openreach cables arriving at the rear of your property and that your main concern.
However, if a change to a FTTP service does not require you to pay a penny more and it does not affect the present contract end date of November then it makes no difference to you if it is a FTTC or a FTTP Service.
That said; I suspect that what you would really like is for Openreach to arrive, (just after you transfer to VM), to remove their existing Openreach Cable, (beit FTTC or FTTP), at their expense because you do not like the look of the Openreach Cable and that is highly unlikely.
Therefore, if the proposed change from an Openreach FTTC service to an Openreach FTTP service, (had not been planned), you would have just moved to VM in November and the existing Openreach FTTC Cable would have remained in place so in some ways the proposed change over to FTTP, (from having the existing Openreach cable, (arriving at the rear of your property), is mute as the existing Openreach Cable will usually remain, in situ after a change to a VM Service and that is a separate issue from the timing of your being able to move to VM without incurring a penalty.
Obviously, you do not have to agree to the change if it alters your contract end date or t&c and if Plus Net do not provide the service you can leave early without penalty.
Personally, I would check what the lead times are to install VM at your property, (I would not agree to change over from FTTC to FTTP, (if the present contract end period and t&c were changed)), and I would arrange for VM to be installed a few weeks before the proposed change date over to a FTTP Service.