Software Deployment

There's no native way of doing this via the installer. You would need to become reasonably proficient with the Windows API in order to achieve what you want. You would need to enumerate all the open windows, checking for the window's title, obtain that window's handle, then send a message to Windows that the window with that handle should not display the 'Close' button.

Needless to say, all that would need to be bundled into a DLL and the relevant function called from within a Custom Action.

Best of luck with that...