Final Fantasy Hacktics

Ok, so I have stumbled upon some fairly hidden pallets that have been done already but atm they are in .png format (I can convert them to .bmp easy thats not a prob.)

Question I have is, how do I compile these different color versions of the same sprites into a single .bmp file so they can be used as generics?

Cause then it would be cool to use to replace a lot of the ugly looking normal FFT sprites.

What is it for? I scourged topics using search reading any shishi editor information I could but never found anything about .shishi file extension?  I am assuming its a package of some sort used by another program?

I checked shishi tutorials before (I am not really new I just never post; I kind of tinker with things on my own time.)

I even google searched ffhacktics topics and forum searched it and nada.

If your wondering what file it is: arena.shishi

I was wanting to recolor some sprites but I saw a topic and saw that it was done. This file is one I saw thought maybe it had multiple sprite pallets within it.