To have the build process use existing usage links, leave the property wt.epm.build.subsumeLinks set to the default value true.

To specify that the build process creates new usage links, set the property wt.epm.build.subsumeLinks to false.

If you want the build process to create new links using your usage link class (a subclass of WTPartUsageLink) set wt.epm.build.linkClass to your usage link class. The default value is wt.part.WTPartUsageLink.