I want to give users the opportunity to click "Reboot" after the ACU when
they are ready, but no option to "Close" without reboot.

I opened setupnw.exe with a PE resource editor and found the "Installation
Complete" dialog (Dialog 137), edited the text and removed the "Close"
button, recompiled and saved. Ran the ACU, still shows up as original
dialog!!! Tried two different PE resource editors (Resource Hacker and PE
Explorer) to no avail. Can't change any dialogs- they all return to
original when run. Even tried removing "visible" property on Close
button, still showed up.