@Antonio **********
I HAVE seen people cancel an extension of say based on "being over 50" (retirement) and immediately apply for a new extension based on employment. NOT all offices will let you do it. You are NOT wanting a new Non-B VISA, you don't need that. You want to change the REASON for your extension from one based on 'retirement' to one based on employment.
I certainly would be talking to your soon to be employer to see what they suggest you do BEFORE you go cancel your current extension