Is there anyway to make zombies not burn in daylight or edit the minecraft reference files as I cant type or edit them. I am making a zombie apocalypse mod.

Use the LivingUpdateEvent. If the entity is a zombie, then check Entity#isBurning() and use Entity#extinguish().

 

That should work.

I'm not certain of the timing of the burning processing versus the damage from fire.  For example, I think while you could extinguish the flame with LivingUpdateEvent, I suspect that other code will run that will detect the light and set it on fire again and then process the damage.  Again, I'm not sure, but I think the LivingUpdateEvent will fire before other onUpdate() code is run, so in this case the extinguishing may get undone.

 

It may be more controlled if you process both the RenderLiving event (to make sure it doesn't display as on fire) and also the LivingHurtEvent (to make sure it doesn't take damage from fire).  As long as you don't see fire, and it doesn't take damage from fire, I think that counts as not being on fire...

I'm not certain of the timing of the burning processing versus the damage from fire.  For example, I think while you could extinguish the flame with LivingUpdateEvent, I suspect that other code will run that will detect the light and set it on fire again and then process the damage.  Again, I'm not sure, but I think the LivingUpdateEvent will fire before other onUpdate() code is run, so in this case the extinguishing may get undone.

 

It may be more controlled if you process both the RenderLiving event (to make sure it doesn't display as on fire) and also the LivingHurtEvent (to make sure it doesn't take damage from fire).  As long as you don't see fire, and it doesn't take damage from fire, I think that counts as not being on fire...

Okay but how do I edit the zombie entity files?

You cannot edit minecraft source files, just do what shieldbug said to do.

Maybe you want to create custom zombie and spawn it instead of vanilla zombie?

Okay but how do I edit the zombie entity files?

 

You don't have to.  We said you should use event handling to do it.  When the events we mentioned fire, your handler should just check if it is firing for a zombie and if it is then do what you need to do to extinguish the fire.