Flash MX 2004.
item.linkageURL
Property; a string that specifies the URL where the SWF file containing the shared asset is located. Animate ignores this property if item.linkageImportForRS, item.linkageExportForAS, and item.linkageExportForRS are set to false. Conversely, this property must be set when any of those properties are set to true. You can specify a web URL or a filename in platform-dependent format (that is, forward slashes [/] or backward slashes [\], depending on the platform).
The following example specifies a linkage URL for the specified library item:
fl.getDocumentDOM().library.items[0].linkageURL = "theShareSWF.swf";