Has anybody done Bus/Coach licence while being a qualified lorry driver? Does it make any difference (can you skip some parts of obtaining it) or are you in the DVSA eyes a new driver and has to go through all the steps - theory tests, medicals, and other bs like a well newbie?
Not necessarily - if you ticked D when you applied for C then that is already covered OR if not then having a D4 medical for LGV within a certain time before applying for D prov will cover it
If got D4 LGV medical due very soon then simply do medical and put D2 form with D ticked in with it and it will get added for free