I know. That's why I wrote:
'What would make it even better/a more seamless UX is if the 'Executing Veil' over the entire screen didn't happen during DISPLAY LAYOUT, or if it only happened over the area of the panel being updated.' (like when a query is refreshing)
But what is amusing is that someone other than me in commenting on UX/UI/elegance/seamlessness.. re., you mentioning 'flickering' not looking professional.
Instead of updating the panel with DISPLAY LAYOUT, what about updating it with a query which has been configured so that no records are returned? (ID=0)
Make the panel a HTML panel which is triggered to update when the process which runs for the button is run, and use a process to update it, which runs a query.
Turn off the Title Bar, Column Headings Row; and Paging Bar, so nothing appears.
The 'Executing Veil' might not happen if you turned it off in the Dialog from which you added the button to the form in the first panel.
[SPEAKING OF WHICH, have you already got it turned off, and despite which the 'Executing Veil' is still happening for DISPLAY LAYOUT?]
If the button is a form HTML cell button which runs the process using AwareApp.startPr.. then it seems you cannot suppress the 'Executing Veil' as I don't think there is an option in the parameters.
OR, you could VIEW a form as the last action in the process, and make the form blank and 1px x 1px and change the color of it to be white so it's not visible.