I'm doing a full-colour magazine cover in PageMaker with a full bleed. I did one two months ago, and it came back from the printer trimmed a bit wider and longer than I wanted. They tell me that I need to move the crop marks on the outputted film in order for them to trim the publication differently.

My question is, how do I move the crop marks (by changing the size of paper to custom and making the page size slightly smaller to suit my cropping needs?) I do the design on my computer here then take it to a commercial place to get it outputted to film and colour key. Is this their responsibility to place crop marks where I need them, or can I do this myself before it gets to them? Please help I'm going nuts!