Hello, attempting to remove existing ship lines from starting fleets is not recommended, you would be better off making your own starter fleet (with a unique fleet_design_name and display_name) and loading it via XMLMod.
In order to do so, navigate to the XMLMods folder in your AI War 2 folder.
Create a new Folder with any name you desire.
Create a new Folder inside of your newly named folder called FleetDesignTemplate
Create a new xml file with any name you desire, and move your example mod code inside.
File names do not matter, and your main mod's folder name doesn't matter, but you require the same Folder layout that occurs in Configuration.
Example: