Hi,
This is not possible yet unfortunately but we are working on it. The issue with those kind of options is that it could create a lot of errors easily. Could you add this demand in the "Idea zone" section of this forum (have a look as well at the other propositions and put a "like" to the ones you would find interesting for future releases).
You can still easily copy user code from one project to another. What i personally do when I know I will use a custom widget/container in different project is to do as much as possible through code. The downside is that you dont have the complete preview in TouchGFX Designer of the project.
/Romain