A word of caution though and it had been part of a recently issued NOTAM in my airline, expect the bus to "nosedive" between 2 hard altitude constraints above the platform altitude and it did happen to me: Initial App Alt
( Platform Altitude ) at 2000 Ft, "intercepted the profile" in FINAL APP at 3000 Ft and the plane initiated a 1500 Fpm rate of descent to change 1000 Ft of Altitude as it was chasing the 2000 Ft constraint. Pretty unpleasant.
We had this problem when first coding the RNP AR procedures, when crossing the waypoint, it would porpose down to the next waypoint alt and level off. Yes, it was quite concerning. This was particular to the Bus.
Makes one check to make sure there is the + sign in front of the altitude, and that seemed to solve the problem. 'at' to the system is when there is no plus or minus coded on the altitude.
Unfortunately, as far as I remember, you have no means to add a "+" or "-" when entering your own.