Temporary car import permit

I know if you take a US plated car south of the free zone you need a permit good for 6 months. I was told you have to take the car back to the port of entry to renew the permit. My question is can you take the car to another port of entry to renew it, or does it have to be the same place you got it.

Please let me know only if you know for sure!
Thanks
 
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