I'm reviving this 4.5 year old post to say thank you for this. I wanted to do something similar, except I didn't need to do anything fancy. I also made this a single-button toggle. For those that may want to do something similar, here's my code:
@ifset:DUAL=on
Set LISTERSIZE 600,700
Set DUAL=Off
@ifset:else
Set LISTERSIZE 1200,700
Set DUAL=Toggle,Vert,Remember
This detects if Dual Lister mode is on and runs the first two 'Set' commands, else it runs the second two 'Set' commands. I didn't need toolbars to be changed (yet), so I left those off. I also wanted it to switch to Vertical dual listers instead of the Horizontal that Ving (Jon) needed. This script runs using the Function set to "Standard Function (Opus or external)" and toggles back and forth on just one button.
Good stuff!