Can you change column formats in child datawindows?

I have a child datawindow in a trailer band of a nested datawindow.  I use modify to attempt to change the display formats at run time, but, while this doesn't produce errors, neither does it change the format of the displayed data.   Should this work?

This is a sample modify string

paid.format="######0.00;(######0.00);######0.00" unpaid.format="######0.00;(######0.00);######0.00"

We are running PB12.5.2 Classic on Windows 8.1