Addons to make turreted ships more agile, at the cost of firepower.

Auxiliary Thruster - Turret
I don't really have any good numbers for how spin torque works in the game, so I'm going to put in that stat as a comparison to the turn speed of other ships.

Thrust: +50N
Turbo Thrust: +150N
Grid: 6
Mass: 500 kg
Max Speed: +5 m/s
Spin Torque for:

Single on an Atlas Type X: Makes an Atlas X with only the AT and a fast-Charge powercell turn as fast as a Warthog Territorial Defender

Single on a Behemoth Heavy Miner (both variants): Makes them as agile when empty as a Centaur basic.

Double on a regular Behemoth: Makes it as agile when empty as a Centaur Mkll

Triple on a Behemoth: Makes it as agile when empty as a Centaur Mklll

Capital Auxiliary Thruster - Turret
Thrust: +1000 N
Turbo Thrust: +2000N
Max Speed: +5 m/s
Grid: 18
This can technically be used on non-capships as well, therefore a high mass to discourage it.
Mass: 10000 kg
Spin Torque:
3 on a Goliath: Makes it as agile as an empty Aeolus Light Behemoth.
4 on a Trident: Makes it as agile as an empty Behemoth XC
Additionally, de-nerf the drop rate from capship large ports, so the newly agile capships can be used for farming, without enabling afk/automated farming that caused a problem before.

This add-on would give more variety to turret addons, with more hauler configurations for ability to defend/ability to run away. Might also give a buff to capship PvP, with more agile capships.

This is an interesting idea, but I think your numbers are way too big. At most, the addon should make the ship feel like a lighter variant, not like a smaller ship.

I guessed that might be the case. Would halving all the stats (except for mass and grid) make it more balanced?

-1 I think if you want agility, fly a agile ship. If you want to move a lot of cargo, expect to be slow.

Somewhat Related threads
Jato Rockets
Make brake mutually exclusive with thrust

I thought there was another suggestion about this within the past two years, but i can't find it.

If the thruster is chemical based (hypergolic or similar. Fuel needs to be reloaded ), and only thrusts in a single direction (for example, designed to quickly cause a ship to do a 180 to 360), then a big +1 from me

So you're suggesting an addon that needs reloads and instantly 180's your ship, without any control in it. Where do you see such an addon being used?
Also, so far all turrets have infinite ammo because it refills just by entering and exiting the turret. In such a situation, limited ammo would just be a minor inconvenience which you can work around in less than a second.

So you're suggesting an addon that needs reloads and instantly 180's your ship, without any control in it.

No, i'm saying it could 180 it, but you'd still have to figure out when to let off the thruster trigger. This makes it a skill based addon.