ICAO Phraseology Reference Guide states :
"APPROACH AND LANDING
Pilot-interpreted Approaches (eg ILS) Phraseology
The phrase ‘cleared ILS approach runway xx’ has, in the past, introduced
some ambiguity whereby pilots have taken this to mean they are cleared to the
altitude/height depicted on the approach chart immediately prior to the final
approach fix. This should not be assumed; normally clearances to descend at
this point will be given distinctly.
Other phrases that are commonly in use include:
‘Report established localiser (or ILS, GBAS/SBAS/MLS approach course).’
‘Maintain (altitude) until intercepting glide-path.’
‘Report established on glide-path"
So it means that you're unable to des without clearance. There were a few reprts from Chinese CAA about the situation the same as your example.
IAF to IF 900м , FAP at 600m during turn to final the flight crew recived "cleared ILS APCH RW..." and descended to 600 w/o instruction to des. The result was a report from CAA. As I know in the U.S. and in countries that also respect U.S. rules ( South Korea for example) it is permitted to des. as published when you recieved Cleared ..Appch.