Interestingly, a Mexican cartel did something very similar for their comms network about 13 years ago (source)
Soldiers seized 167 antennas, more than 150 repeaters and thousands of cellphones and radios that operated on the system. Some of the remote antennas and relay stations were powered with solar panels.
The law allows you to shoot anyone who is trespassing on your property (which is absolutely terrifying). It’s not specific to illegal immigrants and couldn’t be used on someone else’s property. So shooting a rancher on their property would still be illegal.