I don't use the default preview window. I defined my preview window with a global variable for the title so I can set it anytime. Here is the code...

PUBLIC windowtitle
windowtitle = "Custom Report Preview"
DEFINE WINDOW seeit FROM 0,0 TO 50,128 TITLE &windowtitle close system

Now when I want to change the window title all I have to do is

windowtitle = "My window"
REPORT FORM xxxxxxxx.frx PREVIEW WINDOW seeit

I hope this helps.

Bob