How do you remove a default faction from Nexerelin and replace it with another (most likely a mod faction)?
In data/config/exerelin/exerelin_config.json:
Remove vanilla factions from the builtInFactions list to make them not spawn.
A mod faction can similarly be added to the supportedModFactions list to make it appear in the sector (though the ones that are currently supported are all already there; just enable the mods you want before the game starts). Depending on the faction settings (and if you want to play as that faction), you'll have to do some extra work; see the section on adding support for a faction mod in the first post of this thread.
EDIT 1 : Spoiler
java.lang.IllegalArgumentException: bound must be positive
at java.util.Random.nextInt(Unknown Source)
at org.lazywizard.lazylib.MathUtils.getRandomNumberInRange(MathUtils.java:662)
at exerelin.world.ExerelinSectorGen.buildSystem(ExerelinSectorGen.java:1142)
at exerelin.world.ExerelinSectorGen.generate(ExerelinSectorGen.java:761)
at com.fs.starfarer.campaign.save.CampaignGameManager.o00000(Unknown Source)
at com.fs.starfarer.title.OoOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.dialogDismissed(Unknown Source)
at com.fs.starfarer.ui.do.dismiss(Unknown Source)
at com.fs.starfarer.ui.impl.O0oO.dismiss(Unknown Source)
at com.fs.starfarer.campaign.save.O0oO.actionPerformed(Unknown Source)
at com.fs.starfarer.ui.thisnew.super(Unknown Source)
at com.fs.starfarer.ui.H.processInput(Unknown Source)
at com.fs.starfarer.ui.V.o00000(Unknown Source)
at com.fs.starfarer.new.?o000(Unknown Source)
at com.fs.oOOO.oOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.?0000(Unknown Source)
at com.fs.starfarer.combat.D.o00000(Unknown Source)
at com.fs.starfarer.StarfarerLauncher$2.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Ever encountered this before? What does it mean?
Hmm. I'll need to test to be sure, but at a guess it breaks if minimumPlanets in the config is higher than the max planets in the game start settings. You could try lowering one or raise the other.