Renew TN for new office location?

Hello, All

I have a question about the Office relocation.

Currently, I am a civil engineer working in San Francisco, California.
My current TN visa will expire in Feb 2009.

And, I am going to transfer to Los Angeles, California after three weeks, and my title, salary, benefit, and job description won't be changed.

The only differences are the office location and different projects.

Do I need to renew TN visa? company attorney told me that I do not need to get a new TN since I will stay in the same company with same job duties and titles.

Thank you soooo much, guys!

PS. If I need to renew it, then, can I just drive to Mexico, get a new TN, and come back on the same day?