Can't mod the level cap or make leveling frigates.
L10 is the max for all capitals and iirc capital abilities can only go to a max of three levels.
You can make leveling frigates like the [FrigateCombatTurret.entity] which are spawned by ability. They will have stats at Levels 0, 1, 2 according to what level the spawning ability is at.
To make the Frigate Combat Turret move like a ship instead of sitting in space, you change the following:
now you have a spawned/deployable missile turret that moves and can phase jump with fleet -nifty, eh?
To make a leveling Kodiak, you would need to copy the entity file, restructure it like the combat turret, and create an ability that deploys the leveling Kodiak and Levels to 3 instead of 1. As Capital ability levels, the spawned Kodiak MK2's stats change accordingly.
Of course, to edit the file you need the reference data converted from BIN to TXT. Files do work in game as TXT. Great for modding.
We rotten, arrogant bastages involved with 7 Deadly Sins have a few leveling frigates that are spawned by ability. Another modder has tons of ships that are spawned by ability, but again -these are ability spawned ships, not ships built by the frigate factory.
This is a fun way to have a "Builder" capitalship that has 3 abilities that deploy 3 different ships that level as the ability does. If the spawning ability improves from L1 to L2, the ships deployed when ability was L1 don't suddenly improve, but those ships deployed when spawning ability is L2 are now better than those spawned before.