The basics are rather simple.   At least to my knowledge, though nothing i've ever created i'd call sellable.

Basically, create your character with morphs/injections, to the specifications you want it, then in your pose folder just make a new folder, and click the plus sign..... and it will direct you through it in the window to save the morph targets.

I've never made textures so that part I'm unaware of, just saving the finished character.

If you dont want the default non rendered V4 (or figure) in the library picture, render it out, then use the render as your background for the morphed figure.  Move the scene over, out of the picture, then save it.  It saves the morph targets, but uses the background picture as the icon in the library.  Much nicer looking.

err, realized i missed that, i dont know if that method saves inj's at all.  Just morphs.