U can modify the ship classes but not to make new ones.
Destroyers -> like warships, battleships, battle cruisers, light destroyers, battle destroyers, assault cruisers, attack cruisers, etc have the size “cruiser”.
Destroyers doesnt mean to be bigger than a regular cruiser, but for example, they should carry more weapon slots than standard ones. And thats all, the power output should bit a little bit higher, but not too much. More power, and 1 or 2 more standar slots, u get the battle destroyer.
Assault cruisers, they should have a bit more speed, and almost equal number of standard slots and weapon slots.
Attack cruisers, like a regular cruiser but with more weapon slots.
Escort / Support cruisers -> more standard slots, a bit armour bonus.
Flagships (or capital ships) -> more output power, more number of slots (standard and wepon), a bit armour and integrity bonus.
Motherships -> a lot of standard slots and not to many weapons slots (but standard slots + weapon slots = the higher number of slots in any ship), integrity bonus.
Space Stations -> The same number of slots than a mothership, but a bit more weapon slots and more integrity and armour bonuses.
And ETC Maybe we should include only the battle destroyers, battleships, warships and motherships in the dreadnought class. And watch out, cuz some carriers are bigger than a battle destroyer. So they should be included in the dreadnought class too.
The “Dreadnought” word is applied to the ship size, not the ship configuration. U can get a dreadnought like a planet in size but with less weapon slots than a destroyer. Dreadnought doesnt mean “i am the supreme power of the galaxy with my 40 weapons slots”.
As u see, u can “create” a lot of cruiser clases, just keep in mind sometimes the size doesnt matter with a ship class, people forget that “Destroyer” is a ship configuration, not a ship class. For example , a battle cruiser is equal in size than a warship, or a destroyer. A Battle Destroyer should be a little bigger only cuz it is supossed to carry on more output power and in consecuence more powered weapons. I already made a list in EXCEL “inventing xD” more than 10 ship configurations for the cruiser class and the same for frigates and fighters.
P.D.: A Exploration ship it is supossed to be just a frigate with the exploration configuration. It is not smaller than a regular frigate. In fact sometimes its even bigger. So u get fighters, corvettes, frigates. U can make a exploration corvette, but it will be still a corvette.