Unclear Clearance

OK, just to distract you guys from "IFR with a VFR GPS" ---

Flying into Grand Marais MN last week (KCKC) I was out maybe
30 miles at 7000 and got "Cleared for the approach, maintain
4000 until established. Contact advisory ... "

The reason for the early clearance was, I think, that I was
at the edge of Center's radar and comm coverage. (Grand
Marais is near the Canadian border on the north shore of
Lake Superior. There was nobody around.)

But I really didn't want to fly that last 30 miles at 4000
as there were clouds about there and maybe a little ice. I
wanted to stay at 7. So I queried: "Center, that 4000 was
pilot's discretion, right?" and got a "Right."

Did I need to ask? Should I have assumed pilot's
discretion? She did not tell me to descend, just gave me
the altitude limit.