If my understanding is correct (it may not be), it's almost impossible to change something once it's been passed as a proposition in Arizona. The law got changed a few years back because Arizonans got pissed about passing propositions, only to have them neutered or disassembled by the state legislature. So, they required a 2/3rds supermajority or something like that. I was told the details a few years back by a GOP'er whose premise was that one should never vote in favor of a ballot proposition, because repealing or changing them was so difficult.
After all, if the 25 mile rule could be modified, then so could the underlying tenet of prop 203 (state-level legalization of marijuana); and if that were the case, I'm pretty sure Brewer at al. would be at it by now.