All widgets attributes can be dynamicaly defined by a dataProvider and it's se same for menus.
<tabFolder>
<tabItem onFocus="myChangeMenuAction">
...
</tabItem>
</tabFolder>
...
<menu>
<_action>@{dynAction}</_action>
@{dynText}
</menu>
In this case you can change the menu and its actions through a dataProvider that provide a dynAction and dynText properties.
In 1.0.0RC3, you can't customize the popupMenu in an nice way. But the next release will offer the possibility to manage PopupMenu content as a List.