Gas Giants are certainly a vital part of every solar system that will eventually have life; they take on bullies like good big brothars/sisters. Now, I know we talked about plastering layers upon layers of gasses onto 'em, but what about the core, the surface? I've read the planet editor concept (obviously), and am slightly dissatisfied with the lack of customisation described. I suggest we have the ability to fully customise our giants' cores, rocks that revolve around them, storms and other barely needed info. Of course, if the species develops gas propulsion that uses gas giant hydrogen, this might become useful (who doesn't like disecting a solid hydrogen core buried below a hydrogen-helium sea?)
And, also, the physics must be realistic; remember, Gas Giants are not just gas and core, but are actually in different states (gasseous, vaporous liquid, pure liquid, foamy solid, hard solid)

We (humans, not the forum) don't even know how gas giants work. (we have a vague idea, but we do not know each separate process down to the minute detail)

Which means it is impossible to build a 100% realistic simulation.

Also, see:

devblog 5

under "complexity is complex"

Look, we can come up with a model for gas giants, but it'll still be just that, a model.
Which, actually, brings me to a good point. We need the physics people here writing scientific models for systems such as this, so I can plug them in one by one.

wikipedia article on scientific models


TL;DR:

Basically, "This needs to be realistic" by itself is not very helpful. Along with my favorites:

"The physics engine will do this automatically"

"Auto-evo will solve this"

"Eat your vegetables" (actually i love my vegetables, and I don't have a mommy looking down my back at my age xD)

I've got this one, Bashi. The gas giant problem seems complicated, but the parts relevant to us boil down rather nicely, actually.

Gas giants are essentially huge balls of complex gravitational fluid dynamics. The OP demonstrates a fundamental misunderstanding right off the bat - the "rocks" are not floating around somewhere inside it; they're crushed down into the core, utterly inaccessible underneath a high-pressure ocean of metallic hydrogen, and an outer layer of liquid hydrogen. If you were from a gas giant, you wouldn't even know there was a solid core unless you developed the math and physics knowledge to calculate the existence of one. You'd have evolved in the upper, gaseous atmosphere, the same way life lives on the crust of the earth, not down in its mantle. (Check out some grossly oversimplified images of GG composition - specifically, Jupiter and Saturn.)

Basically, it's not worth worrying about.

I'm not volunteering to go and do a ton of research on them, but here's what I think I know about gas giants. The gases on the outer atmosphere "striate" according to density; densest stuff goes to the bottom, and lightest stuff rises. However, the spinning core and metallic hydrogen churns up the layers, giving us cool stuff like disappearing gaseous belts and polar hexagons. This is all heavy fluid macro-dynamics stuff, and to represent it accurately would require a crazy amount of math. So why should we bother?

SINCE we're only dealing with, essentially, a thin layer of atmosphere wrapped around a ball, why treat it any differently than a planet that's covered entirely with liquid water? The only real difference is that the "bands" would be composed of different gases. That's easy to model, I think - buoyancy changes from band to band, the background palette shifts, and the temperature changes. Essentially, it's like a different "continent", or perhaps a different "biome".

As far as the actual editing of gas giants? There's shockingly little to edit. Basically, what you need to know is: How far from its parent star is it? That determines what elements could reasonably be gaseous, and therefore could make up the planet. If it's a proper gas giant (like Jupiter and Saturn), then it's mostly hydrogen; the atmosphere also could contain nitrogen, oxygen, helium, water, methane, and some complex hydrocarbons. If it's an ice giant (like Uranus and Neptune), then it's mostly made up of frozen complex molecules like hydrocarbons; the atmosphere might contain gaseous hydrocarbons, methane, ammonia, helium, and some hydrogen.

I don't think I've ever read any serious consideration of life arising on an ice giant, incidentally.

So presuming you're making a gas giant (not an ice giant), you could, I guess, edit the concentration of different gases in their outer atmosphere; the banding could change automatically as a function of the atmospheric composition. We'd have to do some research as to how that would work, but it hardly sounds insurmountable.