I don't think they'll care about this. Probably only 1% of their customers are capable of "hacking" this. As long as the tablet replace is cheaper than getting a new AC unit from another company it's fine for them.
Yes, which is very sad. Nearly all things go into this direction. I still remember the old days of jail breaking the iPhone, and the cat and mouse chase with Apple.
They would have to put the condition inside shared library .so and use Android JNI. Make it complicated and hide the string tablet model throughout the code, just enough time to frustrate whoever is decompiling the so file.
If they want to really do it wrong (or right, from their PoV), they require the communication with the base station to be signed with a certificate signed by their root CA, and put the private key of that certificate in the TPM.
It will most likely be "How do we restrict this hack" and will eventually get into more restricted/quirky hardware & software.