Not sure about the plans you describe, although the term “introductory” would imply it would need to be a new plan. You could use a different email address to create a new Adobe ID and use it though.
I successfully moved from the introduction 1 year complete CC plan (29.95/mth) to the Photographers plan, then back to 1 year of full that I received from attending PS world, and then back to the Photography plan. Maybe not quite the same as you are describing, but all were pretty seamless.
