If you want users to only be able to create forms in a certain app, you don't need to change dialog-form-setting.xpl
but instead can just update the form-builder-permissions.xml
to include:
<role name="*" app="myapp" form="*"/>
where myapp
is the app you want to restrict users to. And of course, through this configuration file, you can make that restriction more granular, on per-role basis.