Hi Guys,
I got to solve it using a kind of manually fragment extension.
I copied the fragment from the standard project and pasted it to the extension project, renaming it with the "Custom" termination (from "S4.fragment.xml" to "S4Custom.fragment.xml").
After that, I changed the reference for this fragment at the S4Custom.controller.js, at point of fragment initialization (method handleRouteMatched, line 182, from "mytravelandexpense.view.S4" to "mytravelandexpense.TRV_TE_CREExtension.view.S4Custom"), like the source code below:
Finally, I commented the "Add Cost Assignment" button source code on S4Custom.fragment.xml:
So it worked and the button is not being shown anymore:
As the SAP Web IDE don't provide the fragment extension wizard (as it is provided for view and controller), I think this way we work with fragment extension.
Regards,
Jairo Canuto