The post about insurance came while I was typing.
Thats not such an issue here in the UK.
Many places around the world are tighter on modifications.
But since Im running a vehicle that often have modifications done in normal as well as off road performance instancies. Adding a T piece to a vacuum pipe for the "Assisted" brakes wont be an issue as long as I make sure its seen to have been done properly and is secure.
I also have specialist insurance for an off road vehicle and they expect that most customers will have modified the vehicle in some way. Under body armour, roof racks all the way to uprated suspension and brake systems.
An extra guage will not be a problem.
Gordon