Yes, you could add it to any entity you want. But you would need to specify it in the config. This option is located at the end of the file.
Here is the example of how it can be done -
"[Misc] Spawn positions on other entities (full prefab name)": {
"<FULL ENTITY PREFAB NAME (e.g. assets/content/vehicles/trains/wagons/trainwagonb.entity.prefab)>": [
{
"Type": "<SPECIFY THE TYPE (AATurret or MachinegunTurret)>",
// Below you have the relative position and rotation.
"Position": {
"x": -0.01828,
"y": 0.16,
"z": -1.6145
},
"Rotation": {
"x": 0.0,
"y": 180.0,
"z": 0.0
}
},
// you can specify multiple turrets, just copy the above code and separate it with a comma.
]
}