There is the very remote possibility that the Mexican broadcasting powers that be may (SCT?) flex their muscles in retaliation to any major border policy changes...
They could say "Since there's a big ol' wall blocking off access to the US, we will not allow stations in our country to broadcast commercials for businesses in the US..." Poof! No more Tijuana stations broadcasting to the San Diego market!
That being said, the Mexican radio concessionaires know what side their bread is buttered. They'd fight, argue, and bribe their way to avoid any issues with their cash cow "border blasters". And it would be far more likely the Mexicans would prefer to retaliate by messing with US heavy industries doing business there (ex: Ford, Fiat/Chrysler, etc)
Radio-X
The SCT doesn't have jurisdiction here anymore and hasn't since 2006.
The two regulators that could potentially have a hand are the RTC and the IFT.
The RTC's acronym is best remembered as Radio and Television Content (it actually means Radio, Television and Film, but that's not the point). They regulate content, advertising of contests, religious broadcasts, station IDs, and those times when stations have to carry presidential addresses, PSAs and La Hora Nacional. (The RTC manages the distribution system for all of these.) They also rate films and TV shows. They've been a lighter touch regulator than usual in the last few years, but this is still their area. The RTC has no hand in the actual technical operation of stations.
The IFT is the opposite. It is the Mexican FCC. It licenses radio and TV stations, authorizes their technical parameters, and coordinates with the FCC within the framework of the various agreements that govern broadcasting along the border, such as the 1992 Querétaro agreement that governs FM broadcasting and the 1998 Washington memorandum of understanding on digital television. (Note that some of these have treaty status.*) The IFT also has duties in the telecom space, regulating in everything from cable companies to cell phone providers. It cannot, however, sanction stations for the content they carry.
Right now, the Mexican government is still trying to figure out how they are going to react and what this means for them. They're dealing with quite a bit of unrest at home as well.
In a Reforma poll put out today, President Enrique Peña Nieto's approval rating is at 12 percent, and the Morena party (read: Andrés Manuel López Obrador) is leading way-too-early presidential polling with 27 percent. June 2018 isn't
that far off!
*
These agreements extend beyond the broadcast bands to other portions of spectrum.
If that happens, expect every English-language Tijuana station to flip to Spanish. No more Magic 92.5, no more 91X, no more MAX FM. What's the point of running English liners, DJs and music with every commercial targeted towards an XE audience in Spanish?
I could see one or two stations sticking with the format. Mexico has its fair share of English classic hits and English AC stations, particularly in large cities, and they bill well because they reach the high socioeconomic levels.