You can also write a short patch to "disable" the required antenna rating. I did just add a new config file for RealAntennas setting the required antenna rating to zero.
TBH it's a quick and dirty solution, but it's a solution, where you don't need to edit your savegame every time you choose a relay contract.
@Kerbas_ad_astra
Am I allowed to write an instruction for that diy patch?
Or could you maybe just add such a config for RealAntennas into your mod?