Would it be possible to have this as Addition instead of just replacement (Which I am guessing it is?)
haven't tried yet. but if it is addition and not replacement, I will go for it!

I would be open to it. But:

1. It would be a breaking change (I hope nobody minds about that).
2. I need someone to provide an icon for that, so it is distinguishable from the normal thruster (I'm not a graphics designer or something).

Sorry for late reply.
For 1: True it would be a breaking change. You could release it as separate mod and so those who would want that version can run that version (which I do want) thou this brings you the dreadful another task to do when something is updated.

For 2: Icon, You could just reverse the current Icon, or just run it upside down, or just inverse colors (I would run upside icon if I were you. or if you are able to rotate it, just rotate it slightly so its straight up)

I think this is perfect. nice and simple. Please don't change. :)

You can instead of editing the base game prototype, just duplicate, then it changing the fluid box positions, and then its name, i dunno if rll needs a new icon, if you actually wants to change the imaging then it will need some ideas since it has a lot of sprites