As someone said already - if you are given a level restriction, it is for a reason.
FL130 by GWC is pretty cruicial since there are aircraft entering the TMA from other directions at F150 and FL140.
If you are set up on a rate of descent to make a level restriction, and then given further descent before reaching the restriction point, I think you'd be pretty goddam stupid to disregard the previous restriction!
Ok, the official line is that a new clearance cancels the previous, but come on - use some common sense. And remember, it's your own safety your playing with if you don't.
And as an aside - "level GWC" or "level abeam GWC" should be the clearance. Not "level BY GWC" so there should be no ambiguity. That is - at, or abeam GWC your altimeter should already be showing FL130. If you achieve the level 10 miles before or exactly as you reach GWC it doesn't matter. Just NOT 1 mile after...
Of course you can replace this restriction with any you like (FL250, 30 miles before MID for example!) But the idea is still the same.
And finally a question from me to any pilots reading this. What do you think about the condition "expedite throughFLxxx" ? Do you take the word expedite seriously? or would you rather you were asked to provide a specific ROC/ROD? I'm undecided on this and would like your opinion.
Thanks GW