Lets say you have a ship with a flare antimissile system.
The antimissile flare weapon is attached to the ShipBone "FlareBone".
If you now change the flare weapon with a nuklear launcher that was attached on the old unit at bone "NukeBone",
then you need to rename the bone from the launcherblueprint from "NukeBone" to "FlareBone".
Thats all, the weapon should work now.
Now you want to attach a weapon turret to the same place.
A Weapon turret has 3 bones; "PitchBone", "YawBone" and "MuzzleBone".
Because the ship has only 1 available bone for the weapon, you can't add that weapon there.
In this case you need a 3d model program and add 2 more bones or it will not work.