Not in the current Surveyor 1.0 but the ability to set the height of multiple baseboards at once (exactly how many is as yet unknown) is promised for the forthcoming Surveyor 2.0.
One "cheat" you can use is to assign a region asset to your route that has its altitude set at the desired height. This will set the "zero datum" for the entire route to that height with individual baseboards above and below that height according to their relative displacements. Not the desired solution in many cases but the best that is currently available in Surveyor 1.0
Development: Trainz Plus - b117699, Win 10, 16GB, RTX 3060Ti
Testing: Trainz Plus beta - b117669, Win 11, 16GB, RTX 3050Ti