Well if ya ever wanna give it a try, here's how:
1: Add the pig model to ur boar model
2: Make the texture big enough to fit the pig & boar textures in one image
3: Move the UVs for the pig & boar to apply the texture correctly
4: Put the pig texture in (assets>minecraft>textures>entity>pig) named "pig.png"
5: Put the boar texture in (assets>minecraft>optifine>mob>pig) named "pig2.png"

If u want weights though, u need to create a pig.properties file in (assets>minecraft>optifine>mob>pig) that says:
"
skins.1=1 2
weights.1={Pig weight} {Boar weight}
"

If you want biome-dependency, add "biomes.1={Biome name}". This can also be combined with weights. That should be all!