So I did some digging in the code and if you unzip Maraxsis and go to -> 'maraxsis/scripts/project-seadragon' you can reenable the alterative rocket parts by changing the function in line 13 from true to false. Once that's done rezip the file and that sure be it.

Now with that out of the way we can now discus some new alterative recipes for rocket parts. Here's my random spit ball of ideas.
For context you need 50 rocket parts to make a rocket.

Fusion based rocket power.
1 Fusion reactor, 100 barrels of water, 200 Low density Structure -> 100 Rocket parts

Magnetically launched rocket.
4 Heat pipes, 6 Personal battery MK3, 1 Superconductor -> 3 Rocket parts

Space "elevator".
100 Carbon fiber, 15 Barrels of lube, 1 Cargo wagon -> 10 Rocket parts

Space gun.
600 pipes, 1 Power switch, 1000 Explosives -> 50 Rocket parts

I'll ask the Maraxsis mod team to patch it. (So it allows recipe selection when more rocket parts are available).

And unfortunately the game engine does not allow rocket part recipes that output multiple parts; this can however be bypassed by making them externally craftable. I might add a setting for that. But even if I do, I will try to stick closely to the rocket graphics, although I could also add a setting for that XD

Thanks for the suggestion :D