Asking dress maker to change measurements with an expensive costume I ordered?

I ordered a costume about 2 weeks ago that takes around a month to arrive. In that time I’ve lost a little weight so would like an inch or so off the top of the skirt to ensure a snug fit. Would it be cheeky to ask this of the seller? But reassure them that’s it’s totally ok if it has already been made

Asking dress maker to change measurements with an expensive costume I ordered?
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