There's a mod that's already exist for the transport ship:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1442819122

@Reshitelny: Unfortunately, I cannot change the transport ship because I have not found any way to upgrade it after it has been built. You lose the benefit of any customization once it becomes part of a fleet.

Sorry for my English

It works fine in my game, and it's good to know that I can also design my colony ships (wasn't being told in the Description), but I do have a suggestion, can you make the transport ships for armies become design-able too?

It has now been updated.

Personally I like the Idea but the implementation to make this mod more feasible is beyond my current scope.

Does this work in 4.0?

For the custom ships yes if its an auto generated ship they will continue to get upgraded, but if you do get the upgrade icon it would be to retrofit the ship and then it would stop getting auto upgrades.

Honestly thought about disabling the feature all together, I mean how the hell are the ships upgrading all the way out in space anyway and no extra cost, but I'm concerned for the AI.

This was more of a fleeting notion due to something that happened to me in game with another mod, its not really that practical.

Does this disable the auto upgrading that happens in vanilla?