what are the EMC modification to the spawning rules in the nether?

I know for example that on EMC wither skeletons and blazes can spawn everywhere as long as it is on a solid block of nether bricks, and why this was implemented.

Are there any other such modifications?

Examples I am thinking about:
- piglins (non-zombie) normally spawn only in the crimson forest biome or in bastions
- hoglins too (bastions only if with stables)
- skeletons and ghasts are more common in the soul sand valleys
- zombie piglins are the only mob that can spawn on magma

Are these valid on EMC?

I think the netherbrick spawning rules was put in place as a solution to 1.12 nether fortresses as they stopped working in the 1.13+ update

I know

I’ve had all these except for the hoglins spawn around the same area in my nether hub which biome is just nether waste.

Hope that helps a little.

I'm not sure I understand what you mean by "I’ve had all these"

The mobs you’ve listed. They spawn in the nether hub I have built in the Nether biome, Nether waste.