Hi Steen;
No, that is not possible in the current RB implementation. One workaround that I can think of, it to have various RB XMLfiles with different tab configurations. Then you could swap out the current RB for the one that has the full tabs minus one. However, that would be PIA IMHO requiring too many RB definitions with all the possible Tab combinations.
The other approach wold be to write your own PB JSON builder to dynamically build "custom" RB's "on the fly" to match your desired TB Tab combination(s). Again, not a trivial matter.
Even if the PB runtime provided an "X" close feature, the programming would have to account for missing Tabs / Controls when they are closed (destroyed). So that feature would also introduce further headaches IMHO.
All-in-all, I think that the RB Tab close feature would be better handled as a Tab visible / invisible feature when the "X" close was triggered. Further analysis would need to be done first IMHO for supporting that aspect.
Regards ... Chris