Hello and welcome to zeu Bus.
In FINAL APP mode the Bus flies the defaulted FMGS profile with constraints.
In my airline the SOP for fully managed NPA i.e. RNAV app calls for the defaulted FMGS restrictions not to be modified.
The only thing you have to do with the FCU is reset the ALT window to the missed approach altitude, once you are level at your platform altitude or at the profile intercept at latest ( FINAL APP announced on the FMA ).
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.
Bottom line, descend in V/S mode down to your platform altitude while complying with a specific initial descent profile then press APP once you are level at the platform altitude ( VDEV at 1 or 2 dots above ) then arm the APP and watch it doing an excellent job in the final approach.
I hope this helps