a) afraid not
b) will add to the wish list but not sure that the show message being a pop up will be able to support it
but.. other ways you could do this if presenting to a different form isn’t something yu want to do (ie the show url for instance).
Add in a new page to you form that when users invoke what you wanted from the ‘show message’ it takes them to that page.. and a button on that page to ‘back to last shown’
or even set up what you want to show on the form page in a group, and HIDE it by default, then when the users click and the script runs use the ‘set state’ to show it, and a behaviour on the ‘group is clicked’ to hide it again