Are crossing restrictions on an ILS/LOC approach mandatory when flying on the glideslope?
Closest regulatory thing I could find :

ICAO Doc 8168 Section 4 Arrival and approach procedures


  1.7.5 Any constant descent angle shall clear all stepdown fix minimum crossing altitudes within any segment.
  
  5.2.5.1 A stepdown fix may be incorporated in some non-precision approach procedures
  
  5.5.5.2    The  protection  area  assumes  that  the  pilot  does  not  normally  deviate  from  the  centre  line  more  than  half-scale 
  deflection  [...]   more  than  half  course  fly-up [...]  could 
  place  the  aircraft  in  [...] airspace where loss of protection from
  obstacles can occur.


The writing leads me to believe that a precision approach should not contain stepdown fixes, and that the descent should be a continuous descent from FAP to MAP.

Then again, I could find nothing specific to prevent anyone from inserting an altitude restriction in a precision approach.

I cannot imagine what would be the point of coming down on a constant GS only to level off at 1000' then try to re-capture the GS just two miles from thouchdown. Talk about a stable approach...