Apply Network Settings: Don't add computer to Domain if computer exists.....

I'd like to do this:

Create two "Apply Network Settings" tasks: "Task1: Add computer to Domain" and "Task2: Add computer to WorkGroup"

So, I need before to check if computer exists on domain, and configure a additional variable "ComputerExistOnDomain" that has value 1 if exist or 0 if not exist. I suppose that I've to create a package with a *.vbs to do this and apply this task before Task1 and Task2. Task1 and Task2 will have a condition by "ComputerExistOnDomain" variable

How could I do this??