Multiple instances using 'open -a'

I can run 2 instances of my app by launching the 2nd using open -a. Now what I would really like to do is make it easy for me to visually differentiate the 2 instances by giving the 2nd version a different icon.

Could I make a new icns file and somehow assign it with the -b option which is "Opens with the specified application bundle identifier". I'm guessing the bundle identifier includes the icon? Is this possible?

Thanks in advance for any help.

 

I'm using Ableton Live. I use the duplication technique at the moment but then I came across this -a method. The app is nearly 2GB in size and gets updated quite often (and has a script inside the package that independently needs updating often). Would be nice to have just one copy on disk that get instantiated twice.