While working on creating a mod with mekanism support i ran into issues concerning the addition and usage of new gasses, using MDK 8.1.9.265.

NEI crashes the game if a gas isn't set to render properly, looking at the MekanismRenderer class, I thought I would just need to implement the onStitch event:

@SubscribeEvent
public void onStitch(TextureStitchEvent.Pre event)
{
if(event.map.getTextureType() == 0)
{
GasRegistry.getGas("siliconCarbide").setIcon(event.map.registerIcon("nuclearscience:silicongas"));

GasRegistry.getGas("carbonIron").setIcon(event.map.registerIcon("nuclearscience:pigirongas"));
System.out.println("[nsconstruction] stitched gas textures");
}
}

However in game no icon renders for the added gasses, and NEI crashes whenever a recipe using them is veiwed. Just to note the crash report was from a compiled version and not in the eclipse test environment.

Crash report:
https://pastebin.com/Na2s0MtF

I'm not familiar with the 1.7 branch, but on newer versions you simply need to register the gas before the Stitch happens, with a valid texture location set, and the registry should handle it for you.

That said, Mekanism 9 exists on 1.7

Looks like Gas.setIcon.

I'm not so familiar with 1.7 rendering, sorry

How would you set the texture location, I'm really new to using the API, and I can't find anything about this.

Would you know how to initiate the IIcon?

The way base mekanism does it is with event.map.registerIcon(), which is only called through the TextureStitchEvent.

Make your own event handler?