Anything is possible. But not always proper. Myself which is all I can speak for, think it's not a very good idea to mix pre-cut lace and lace you cut from the hide.
A splitter can be made from a simple piece of wood and by using a utility scraper, you can split lace that way.
I myself, no matter the quality of the hide will split my lace for evenness. The quality of the braid you do starts with the hide. It always will. To me a good quality hide is a hide that is without blemishes on the skin side and very little stretchy parts on the outside parts of the hide. Increasing the chance for even more lace that way. Of course as you start to buy your own hides, you'll see what the differences are between each hide. This is an experience best taught, or learned by doing and seeing for yourself.
Brian...