So lately I've been wondering how to simply combine two different hairstyles? What I mean by that is making something like this, where you take two different parts of a hair mesh and make it into one. I tried finding a tutorial for it but I can't find anything on it. Thanks!

I'm not a hair expert by any means what so ever but you'd have to frankenstein the mesh parts together in a 3d program like milkshape and make the different morphs and lods. I typically use the sims 2 vertex data merge and the sims 2 data normal merge to join the verticles together (joining the meshes in a seam) in milkshape. Hair meshes are often made of tons of different layers so you would probably have to fiddle to make it look good. Besides the mesh you'd have to fix the UV map, all the textures and maybe the bone assignments. I don't know if there's a tutorial on how to frankenstein specifically hair meshes but there but there are some for clothes and I guess it would be at least similar for hairs Google might give you more tutorials too.
http://modthesims.info/showthread.php?p=3915605
http://modthesims.info/t/397088

I'm not sure if this is the simple method you are looking for though but I hope it helps