Greatly depends on the type of riding you'll be doing and the type of tires you have on. If they're full-on sport tires, it's highly unlikely they will last that long.
France and Spain should have perfectly respectable places that will change tires for you. So don't change them now.. just ride till they need replacing. It may cost you more to replace them there, but this way you won't throw away a perfectly good set you have on now and you'll save cash in the long run.
+1 on what Eric said...
But if you could, I would change the tires in Spain, as France has ridiculous high prices for tires....
I know, as I needed 2 new tires for my car when I had one to blow on the freeway....
Damn, they know their prices

And they couldn't find the needed tire size first, so they needed to get some from a few hundred kms away

And they didn't balanced them either.... (Thank you for that, French Autoroute security :dissaprove

.
Spain is (a lot) cheaper than France in general, and they are a lot friendlier as well.
But be carefull for their
siesta; if you need new tires, get them in the early morning, or rather at the late evening. Between noon and 4-5pm 95% of all places will be closed!!
Grtz,
Degake
Grtz,
Degake