Our condos' rooftops don't have lightning rods per se, but they do have satellite dishes and AC units mounted there as well. Would these, if properly grounded (and these should be) act as lightning rod "hacks?" This question just hit me like, well, a bolt of lightning !!
Lighting is a lot of energy dumped in a small amount of time. The grounding wire used (most likely from the existing power network) is most likely not rated to handle that kind of surge.
Proper lighting rods and their grounding wires are very generous in their current carrying capacity to minimize the energy absorbed due to internal resistance and heavy enough to make sure there is enough thermal mass to stay cool enough to not melt the wire and/or set fire to your house.
The magnetic field of a lighting strike may trash any "loops" nearby, with hundreds of volts induced into that loop.
For example, assuming the strike has 50,000 amps with risetime of 1 microsecond. Run your grounded rod 1 meter away from the A/C control board, with no intervening magnetic shielding (no steel plates or cases). Let the A/C control board have 4" by 4" (0.1 meter) loops on the PCB foil. How much voltage gets induced into that loop, given a worst-case 3_D topology? Use the formula
Vinduce = [MU0 * MUr * Area / (2 * pi * Distance)] * dI/dT
which simplifies (with MU0 being 4 * pi * 10^-7 Henries/meter, MUr = 1) to
Vinduce = 2e-7 * Area/Distance * dI/dT
Substituting, we find
Vinduce = 2e-7H/m * 0.1meter*0.1meter/1meter * 50,000amp/uSecond
Vinduce = 2e-7 * 0.01 * 50 GegaVolt/second = 2e-9 * 50 e+9 = 100 volts induced into the ground-foil loop of your A/C control PCB.
Thus huge currents flow, and the PCB may get vaporized.
Summary: keep the GND rods away from electronics.