so the short answer is...YES,you do need to cut the traces to install the optional +4db pad network on the balanced inputs of a BP25...it works fine,the values given on the schematic appear to be correct and the level is properly reduced,if one ever needs this back to factory a simple wire jumper can bridge the gap in place of the removed resistors and return things to normal
as a standard disclaimer, it should be said that this really is something that should probably be done by Bryston for warranty reasons... a BP25 is not a cheap investment and most would still be under warranty...if you need this installed,weigh your options and impatience to have it done carefully before proceeding...my BP25 is long paid for and my impatience won
the long answer? this IS simple,a sharp Xacto knife is all you need,the traces in question are easily accessible in wide open spaces and not at all crowded by others,if after looking at the schematic and board, you need more instruction than that,frankly you're in over your head and shouldn't be attempting this yourself...
being that relatively few people would ever need this modification,i'm grateful that provisions for it were included on the board at all,as this IS the proper place to do this...and i can see why the parts were omitted and the PCB designed the way it was,instead of say just having the unused network installed with some way of switching it in or out ...this way eliminates a few connections in the input path while still allowing for the pad network to be installed if needed...and tho maybe not super elegantly so,it's still removable as well.
the best part,besides the volume control working normally now is that my source sounds noticeably better as well,it's not on the verge of overloading the preamp which now has some headroom to work with...this has been a good thing