Asda, 2 ways. Either don't clear down for all the descent, or just say be FL210 or above 25nm B4 XXX (or cross Y FL210+). This is very rarely used, but an example is when you are going balls out and have the base of CAS restricting full descent, give a "not below FL until passing" means only one descent clearance and you can get overloaded else where
Nitefiter - getting down early is fine, if you are given full descent clearance then no conflicts occur,. The reason we give restrictions is to keep you up high as long as you want, but then get you down to the levels we need at certain points.