Is there anyway to flip a texture without having to flip it inside an editing software and save a new image?

Yes, that's why they have UVs. They can be reversed.

Hi

 

You'll probably find this link useful

http://greyminecraftcoder.blogspot.com.au/p/list-of-topics.html

 

Look under the "Block Rendering" sections

 

-TGG

Being new here... but, why not use separate images? The trade-off being of course having to maintain that image flipped around in different ways AND the client having to load multiple copies of what otherwise can be handled (as previously mentioned) with simplistic UV manipulation. I do think the UV approach more elegant because you can also play with other factors such as scaling and normals but i digress (UV is how I would do it-- can be just darn confusing).