Thank you for your message. Sorry that it took long to get back.
Not too soon unfortunately but the development team is now considering the way to add this feature in Astah and would like to ask you if the following limitations are acceptable:

While the activation bar is hidden, you cannot
- create the sub messages ie 1.1 Messages of a sub message of 1 Message and
- create Reply messages

Would these be acceptable?

Thanks,
SJ