I would second the advice to ask at check-in for the earlier flight (presuming you haven't booked a non refundable hotel room at the Pan Pacific or the transit hotel they have airside at KUL) and also asking again at KUL. If you have checked bagagge they may be reluctant to change you over at KUL though.

I have booked a room at the Pan Pacific a couple of times with a sizeable day time transit. This was a while ago now but it was quite cheap at the time so unless things have changed I don't agree that it's expensive.

I would also disagree that KUL has good shopping. It's quite limited although they have been improving it in the last few months. There are a few bars and restaurants but you'll get bored with a 9 hour layover.

Personally with a 7-9 hour layover I would get a room in the Pan Pacific or go into the city for a few hours.