In an attempt to clarify the position, I have been onto Motability live-chat.
The agent there didn’t know whether factory fitted options are covered or not, and gave me the link for RSAM live-chat; stating they are the ones who cover the cars.
The agent at RSAM didn’t know, and told me to contact Motability; as it’s their car and they will agree to any options.
When pressed further, and when quoting the relevant paragraph, confirmation was that “Anything you fit without Motability’s consent is not covered” and also “Motability will only agree optional extras that benefit the user” and then “If Motability deem the optional extra you choose as not essential, they will not approve it, therefore it will not be covered”
So. Beware, and check before-hand.