i have the same your dreams and i am into the same situation. also most trigged cause i need to make some kind of action RPG , so i need to add a lot of code for adding RPG stuff features.
You need to replace ALL Star Wars Asset and not sure that something can be really replaced.
on Openjk source code, (not original JK source code realesed into 2013), the copyrighted stuff chunk of code shoul be removed, and it's on GPL. if you want do that, you can do at your risk, but guys are right, be careful about disney.
rename and remove from code ALL star wars calling, all Star Wars referecens about lightsaber, weapons, force powers, etc for be more safe.
(so for example, calle WP_SABER inrto another way, and FP_DRAIN into another way, and rename the AI stuff related to star wars creatures.
only for this you need to rename and search a TONS of networked functions and this require a lot of preliminar job, there also a lot of limitations of gameplay and engine that avoid you to make HD stuff. (npc limit, vertex limits of models, Shader limits, weapon number limitation, force power limitation). you need AT LEAST to write new libs like .SAB files that allow you to customize weapons and spells stuff, so you can add new weaposn and force power as you wish. the more close things in that way that nicely improve the engine is the JKG jedi knight galaxy project, but it's only for multiplayer arena deathmatch.
PS: however, if you change in code all star wars referecenes and replace all SW assets you should be relatevely safe if you not use that for do cash or money. so some kind of free game.
at least this is about how to works copyright here on Italy, but on UK and USA country things can be much more restrictive and complicated.
on my country depend. in the north region copyright have a lot of importance. on south regions is "no one look no one care". consider that latin countries laws about author rights are a lot different respect to UK \ USA laws . latin countries should be little more open about these things, but not sure. talk with a lawyer of your place or a trusted lawyer of your family before do anything.
i already got 3 legal opinions for my own, and i should be okay, but, as i told, on my country things works little different.