Of course you can. At 3000ft were cleared for the approach so once you're established on that approach you may descend with it. I think the more relevant question for the OP would be, can you descend to that 2400ft platform once cleared for the approach, perhaps even whilst still on an intercept heading?
Spud3, I understand you simply want to know if it's permissable. My common sense tells me it's not but it seems, I may be wrong. In the uk we are often cleared for the localised RXX, whenvestablished descend with the the GS. I always thought this was strange phraseology. Why not simply say cleared approach? Surely it's the same thing? Maybe this thread holds the answer, maybe a clearance for the approach does clear you to descend at your discretion implicitly. I'm yet to confim it either way. I'll continue the search.