You may want to add a custom death message, because right now, when you die from Molten Limestone, it says the player swam in lava, which is untrue

@satanicsanta in which version?

I believe I was using 1.0.6 at the time.

It will not be easy to change that.

The lava death message is managed at entity side, not at lava side.

I have created a new Death Message for the molten limestone but I didn't find where to attach it the molten limestone fluid so far

I don't think it's possible, as wisthy said the effects lava has on entities are managed by the entities (great job there mojang, really) so we can't change the damage type.

Otherwise it would be as easy as writing that line of code https://github.com/Ephys/Omnifluids/blob/cbb73ba5c9fbe9c5d368e6d0324bf033808ab4fd/src/main/java/nf/fr/ephys/omnifluids/common/compatibility/FluidEffectAcid.java#L24

or we have to avoid using lava as "model" and start from scratch with our fluid.

I assumed you do that^ anyway. I've yet to look into the code for this particular mod.