[1.16.5] Changing how a specific block is rendered.

[ThePiekar]

So i have been trying to implement a fluid that flows up instead of down.
I got the mechanics right, but the look is off.
The main problem is: 
the model that is rendered, depending on the flkuid height (the thing that makes flowing water into slopes)
is kinda hardcoded into fluid renderer from what i see (although in a perfect world it would use a model declared in a flowingfluid class).
And to make it look not as bad, I'd need to either somehow supply a custom renderer for my block (or FlowingFluidBlock to be precise)
or add a check in the fluid renderer for if the fluid is a instance of my block and patch a custom function in there.

Neither of which are trivial, from what i can see at least.
My question is, is it doable to lightly patch a core class or pass a custom renderer to a block within forge?
Or by any miracle if theres a way to somehow influence the rendered model from within fluid class afterall?

And yes im quite aware, that you never should modify base classes, but I can't find an event I could intercept to achieve the same result.

[ThePiekar]

Got it working with mixin for now, can't tell I'm satisfied with injecting a custom block check into a random renderer function, but as long as it works it's good I suppose.

For future reference, I hijacked the render fluid function within BlockRendererDispatcher if I recall correctly.