A. Make sure you put your mod folder and files in the right place.

A. Make sure you enable your mod in the in game mod menu.

B. Make sure you are editing the right ship entity file.

You should modify the associated files as it mentions in the documentation of forge tools so the game engine knows there is a difference from the original capital. Re- name the new capitals entity  file, for example  the Tech battleship's is "CAPITALSHIP_TECHBATTLESHIP". Change this to "CAPITALSHIP_TECHBATTLESHIP-B". Within it re- name the

NameStringID "IDS_CAPITALSHIP_TECHBATTLESHIP_NAME"
DescriptionStringID "IDS_CAPITALSHIP_TECHBATTLESHIP_DESCRIPTION"

so that they correspond like this

NameStringID "IDS_CAPITALSHIP_TECHBATTLESHIP-B_NAME"
DescriptionStringID "IDS_CAPITALSHIP_TECHBATTLESHIP-B_DESCRIPTION"

Then go to the string file, locate

StringInfo
    ID "IDS_CAPITALSHIP_TECHBATTLESHIP_NAME"
    Value "Kol Battleship"
StringInfo
    ID "IDS_CAPITALSHIP_TECHBATTLESHIP_DESCRIPTION"
    Value "A heavily armed and armored warship that has many direct combat abilities."

should be about not quite half way down the file. Change the entries to correspond like this

StringInfo
    ID "IDS_CAPITALSHIP_TECHBATTLESHIP-B_NAME"
    Value "Kol Battleship"
StringInfo
    ID "IDS_CAPITALSHIP_TECHBATTLESHIP-B_DESCRIPTION"
    Value "A heavily armed and armored warship that has many direct combat abilities."

Then open the PlayerTech entity file Change the name of the Tech Battleship to that of the new name you have for it.

Then do the same in the entity manifest file.