So......I think I figured it out.
I switched from Visual to AML view and edited the code to include a variable that holds the value of the priority:
PRIORITY="%v_emailPriority%" />
This works - I ran the task 3 times, each time changing the variable value to Low, Normal, High and each time the email received showed the correct priority.
However, if I edit/save that step in Visual view after making that change, it will automatically reset the AML code to:
PRIORITY="low" /> and I have to correct it in AML view.
Can this be addressed in a future release as a fix or enhancement?