How to create an custom item template (eg. content type) that can be only used in SharePoint solutions ?
Rex - if I'm understanding your question correctly, you want to customize an app on a sharepoint page, and then make that customized version a template so you can add it as content to other sharepoint pages?
If so, get your customized app the way you want it to be as a template, then while in the Settings for that app, there should be a link under "Permissions and Management" that says "Save [content type] as template". After you have named and saved the template, you should see it as an option in the list the next time you go to "add an app".