Appendix I, rule 7k covers the brake lines and rule 15 covers how to switch off the ABS if needed.
Both rules were formulated about 2 years ago and went through the rule change process and went into the MoMS in August 2015.
Rule 7k is very open allowing any alternative specification and/or non OEM items.
Rule 15 was required following testing of both the KTM and Yamaha ABS operation under racing conditions. Both systems were deemed to be un-suitable for racing use.
For the KTM it was simply the click of a switch to turn off the ABS, but the Yamaha does not have this facility so we had to create a rule to "allow" riders to modify their bike by removal of the ABS fuse.
It was the view of the group of people that set up and reviewed the lightweight production rules that brake lines have been present on motorcycles for many years and as the precursor to the ABS, are not considered as part of the Ant-lock Braking System hence the brake lines can be changed as the rider requires (bypassing the ABS components if desired).
The physical components of the ABS are to be left on the bike so that there is no advantage gained by removing weight (and also it the ABS can be put back together if the bike was sold for road use at a later date).