Car components spawning scripts

[kia95f]

Hey guys, I know how to make a component (EXTRA) always spawn (like police lightbars), but how do you make a specific component NOT to spawn ever?

...or I know how to group some extras to spawn together, but how can I define a rule like this one for example:
-Extra_3 requires extra_2 and extra_1 to spawn;
-Extra_2 only requires extra_1 to spawn;
-Extra_4 also requires extras 1 & 2, but extra_4 cannot load along with extra_3

Shouldn't there be a mod specifically for EXTRAs to set custom defaults? (And not by trainer I mean)