Dpsweeney29,
As you noted, XP's activation has a certain amount of tolerance, but with that last change you exceeded the tolerance.
Start the Activation Wizard and choose phone activation. You will go thru an automated process that might also refuse activation. If so, choose to speak with a rep and answer the rep's questions, calmly explaining the changes you have made over the course of time.
As long as the rep determines that you have not installed this copy of XP in contravention of the End User Licensing Agreement, they will issue you a new activation code.