how to change the installation location to an external drive
I want to have choice of program installation location
Depends on the App. If it runs an installer, it might offer the ability to choose the location. If it doesn't, it probably can't install on an external drive because it needs to modify the system to work correctly.
If it is a Drag and Drop app, just drag it to the External instead of Applications.
I don't believe there is any way to install an App Store app to another location, but you might be able to move it after downloading.
I was able to move an App Store Arcade Game to an external drive.
To move an item via drag and drop, hold down the command key when you drop it and it will move the file as opposed to copying it. If you hold down the command key and the green + badge does not disappear, you cannot delete the file from its original location.