...combining color plates can be performed in the ink manager, either at output to postscript and pdf, or inside indesign itself...
...this is known as ink aliasing...
...the ink manager inside indesign is found in the color swatches palette flyout menu (top right of palette), in that list is the ink manager...
...the ink manager is also found in the print setup and pdf export dialogs...
...in the ink manager you select the ink you want to alias to and choose the new color you need to map it to via the pull down menu at the bottom (ink alias)...
...when doing this inside indesign you won't see it change unless you have overprint preview turned on, you can check the plates in the separations preview palette (window > output > separations preview)...
...do note that the ink manager is great for a lot of work, but i have come across situations where it fails with imported PDF files, so use with caution. It also won't allow you to map default process colors to a spot color, you need high end rips to achieve that...
...the ink manager is also part of acrobat pro...
andrew
