Like Nico said .
Your temporary vehicle import permit (in anglo short speak the TVIP) will be valid for 180 days .
You must also pay a REFUNDABLE security deposit of several hundred dollars when you buy the TVIP . If you do not cancel the TVIP before it expires you will not get that refund .
To avoid that loss go to one of the border crossings and cancel the TVIP, collect the refund and then store the bike in Mexico in any one of the towns in the border zone or all of Baja .
You can arrange with BANJERCITO to leave it stored in interior Mexico while the TVIP expires but you will not get the refund . When you return contact them again and they will issue a permit for five days to give you time to go to the border and remove the bike from Mexico . Once you have officially done that removal you are free to turn right around into Mexico and buy a new TVIP and again put down a new deposit . .

PS: I should add that by "turning right around " I do mean exactly that . There is no requirement to actually step across the border into the USA. You are in a Mexican border town and you are free to find a hotel , free to ride and walk around in that border zone for an other 72 hours. You are also free to put away your cancelled documents and to walk right back to Mexican Migracion to get a new FMM and then to Banjercito for the new TVIP.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93