Follow these steps to deliver a site template customized with a custom assemblies (web part, event handler etc)
- Save the site as template to generate the .wsp file
- Import the solution in Visual Studio 2010 to create a new project
- Next, right click on the package to open Solution Designer
- In the advanced tab, you can specify new assemblies (ensure that they are included in the project)
- The default features can also be modified in the edit options of the features. The properties specified here will overwrite the existing feature properties
- All set, simply create the package of the project and deliver the wsp file.