Hull Specific/Only Ship Components?

I don't believe that there is a direct way to do what you're asking. However, it is possible to include both flat and multiplier type bonuses to the same attribute using the same component, and I believe you can also add such bonuses to the hull types, which suggests several possible workarounds.

1. Edit the hull stat definitions to add a flat bonus to serve as a base value and a multiplicative bonus of -100% to the same attribute. When you design the components, have them give a multiplier-typed bonus of +X%; the modifier only matters if the hull or some other component on the hull provides a flat bonus to the attribute you're modifying, so any hull that lacks the hidden base value or a component providing a flat bonus of the appropriate type will gain no benefit from the module. Has the issue of preventing flat bonuses of the types selected from functioning on the hull.
2. Similar to above, but reversed; give the hulls you want to be able to use the component a multiplier-typed bonus of +X% to the attribute you want the component to modify, and then give the component a -100% multiplier-type bonus to the attribute as well as a flat bonus to the attribute. Has the issue of making flat bonuses from sources other than your special components more powerful. Has the advantage of preventing newer versions of the component from stacking with older versions of it, if that's something you'd like to block, and also makes the component effectively one-per-ship even if you don't set the one-per-ship flag.
3. Put a -100% or greater "bonus" to the attribute you want your special components to use on the hull types you don't want your component to be usable on. Has the advantage of you not needing to bother putting both types of bonus onto either the component or the hull. Has the disadvantage of disabling all components that apply the selected attribute rather than just your special components (though perhaps you might want that anyways, depending on exactly what your goal is with the special components).
4. Don't want to put +/-100% multiplicative modifiers on anything? Try putting a -X% bonus on the hulls you don't want to use the component, and a (X - 100)% bonus on component in addition to a flat bonus for the statistic to work on. For example, -50% jamming on huge hulls, and your special tiny thruster has -50% jamming (so -100% jamming if mounted on huge hulls) + a flat 15 jamming (net of 7.5 jamming if the only multiplicative modifier in effect is the one on the component). Has the advantage of not completely disabling components that provide the statistic and are not your special component. Also has the advantage of disabling or discouraging stacking newer and older versions of components (especially if the magnitude of the penalty multiplier is great enough; a multiplier of -(1 / X) or more on each component will result in seeing no bonus when you mount all X components in the series, for example; lesser penalties will discourage stacking older versions of components but will not necessarily disable it or make it strictly worse than not stacking the components). Has the disadvantage of being somewhat unclear as to what the actual effects of the component are, especially if you use some of the less commonly-known fractions - for example, how much jamming do you get with a component that has a flat jamming bonus of 0.36 and a multiplicative jamming bonus of -0.17? Answer: about 0.30 jamming (30%). A lot of people would probably need a calculator to determine that; not everyone remembers that 1/6 ~= 0.17 (~17%). Has another disadvantage if you're playing with an attribute which already has a large base value or can get a large base value from other components and your component modifies both the base and the multiplier; for example, an accuracy booster that has a flat accuracy bonus of 10% and a multiplicative accuracy penalty of 10% is worse than useless for lasers, for example (base accuracy of 1 + 0.1 from the booster gives a base value of 1.1, 10% of 1.1 is 0.11, 110% - 11% = 99% => I would have been better off without the accuracy booster), has no effect on missile accuracy, and slightly boosts mass driver accuracy (from 80% to 81%, not all that great; adding a second such booster drops it back down to a net of 80% accuracy, or no change from the base value). A further disadvantage is that depending on the attribute chosen, the component effects may be displayed in a confusing manner even if the net effect is advantageous (a jamming component that offers a 0.1 flat jamming bonus and a -0.1 jamming multiplier, for example; the displayed bonuses are both going to be percentages, so it won't be clear that a ship without other jamming modifiers that mounts this component will end up with a jamming of 9%). Using penalty multipliers more positive than -0.5 can also be an issue as you can run into situations where adding more of the components is actually harmful rather than helpful or even just wasteful (for example, with +X/-10% per component and a base value of 0/0% on the hull, the total benefit peaks at five components and goes down with every component added beyond the fifth; rounding, as occurs with strategic speed and sensor range, may blunt this to some degree and make a few components around the peak merely unhelpful rather than harmful).

There are probably some other possible workarounds not listed here. None of these will work for the proposed fixed heavy weapons (your "spinal mounts"). All of these have some degree of clarity issues, as far as letting the player know what the component will actually do when mounted on the ship.

Yeah i was hoping for something along these lines for tiny ships a swarmers component that would add +1 buffs for each ship in fleet with the same component