I feel your pain.We wanted to make changes too but told that after PWC no changes allowed and we weren't told of any options.Really disappointing of HBC.
I asked for all upgrade options and prices before pre-start and they happily obliged ! We knew which changes we wanted to make by the time we got into the consultation!
This is our first build and never done anything like this before ! But as with any major financial investment! Do the research and know your options !