Hi It's not a difficult job. I would suggest viewing a video by Ronny Shavers here:
Very careful when re-installing the door card and make sure the clips are lined up at the insertion points. No need to pound the door card to make it "lock in".
Once the door card is off, unscrew the door lock knob and you will notice a few fasteners along the bottom of the wood to remove it.
My advice: save the old door cap. The new one will not "match " the other ones even though it may appear to be the same. RR book matched the veneer on each door cap individually and side to side in the cabin.
Thanks for that and yes, I did know that Rolls Royce was always particularly proud of how their woods matched all over the cars. But I have checked and the replacement doesn't look too far off; also, the airbag cover has popped off at some time and that piece of wood has been replaced with quite a bad match. I might almost like to change that piece of wood itself for one that will (now) match the door capping!
The job itself doesn't look too daunting as you mention but it has enough steps to make it more appropriate to leave to an expert who will know or remember where all those bits went.
While I am in there, I wonder if it might be worthwhile upgrading the speakers (on both sides) to improve the sound? I already put in an Alpine PwE-S8 subwoofer on the rear parcel shelf to isolate the sub-frequencies and prevent them from going through the door speakers and the sound is completely transformed!