JED 1.6.0+ - Separate world border

{
    "dimensions": [
        {
            "dim": 123,
            "worldinfo_onetime": {
                "BorderSize": 2048,
                "BorderSizeLerpTarget": 2048
            },
            "jed": {
                "WorldBorderCenteredOnSpawn": true
            }
        }
    ]
}