In the console commands there should be a command setrelation or something. I rarely use it as I prefer to build a relation with a faction before starting my empire and watch everyone else burn or get annihilated by me once they point their guns on my direction.
If I'm not mistaken, the format of the command should be "Setrelation -insert faction 1- -insert faction 2- -relation points here (adding a negative will give them negative relation)-"
Ex. setrelation Player All -100. This will cause everyone even the remnants to hate you.
If it that command I gave you didn't work, you can try typing "Help all" to show you the list of commands for the correct one. Also, since you are using Nex, you can try doing covert prisoner reparations to increase your rep with a faction.
