Do I have to get a recertification if I put a boron lte module on a pcb with a couple of relays and a couple of connectors and a 12v to 5v step down voltage regulator? And any advice on product liability insurance would be greatly appreciated.
Yes, but as long as you use the Particle-certified antenna, you only should need unintentional radiator certification, which is the least expensive and easiest to obtain. This page may be helpful.
Essentially the unintentional radiator test certifies that your combination of components does not emit unexpected RF.
If you have high voltage relays (over 90V) you could require other certifications such as UL in the United States.