If it was actually repaired and not replaced with a refurbished unit, it is irrelevant. The unit is still registered from when you did it originally.
If XBOX replaced the unit, they should have automatically updated your account with the new console number. On the off chance that they did not update, then you need to contact XBOX and have them update your records so that the warranty is still in effect. (assuming that your original console is still under warranty.)
If your consoles warranty is due to expire in less than 90 days, XBOX will also extend it up to the 90 day mark if they replaced your system with a refurbished one. References : Personal experience
it will automatically be updated for you.
References :
If it was actually repaired and not replaced with a refurbished unit, it is irrelevant. The unit is still registered from when you did it originally.
If XBOX replaced the unit, they should have automatically updated your account with the new console number. On the off chance that they did not update, then you need to contact XBOX and have them update your records so that the warranty is still in effect. (assuming that your original console is still under warranty.)
If your consoles warranty is due to expire in less than 90 days, XBOX will also extend it up to the 90 day mark if they replaced your system with a refurbished one.
References :
Personal experience