FCC compliance nRF9160 external antenna
I went several times in an Italian EMC compliance test lab for some tests and asked them a similar question regarding pre-certified modules.
The answer was:
if you put a certified module on a new system you save the most expensive tests of the certification but some tests must be done again.
For example, the output power test must be done.
If the new system has a built-in antenna, the output power test is done in a semi-anechoic chamber.
If the new system has a connector for the antenna then the test is done by a spectrum analyzer. No chamber.
If the new system has a connector and it is sold without an antenna, then the output power test must be done by the one who buys the system.
Nordic's modules are certified using a host system which is different from yours.
They told me: even if you copy the Gerber files and all, your host system is different from the host system that led to the certification of the module.
Hope this helps.