No, you can not register offspring as a half mini, just the same as breeding an AMHR mini to an AMHA only mini, the offspring is not registerable. There is a pinto registry, and there are CDE (combined driving events) they can be part of.
You may choose to do whatever you want with your mini, horses with great, steady heads on their shoulders make for level headed animals........but if it were me, all i can say is there are so many with papers going dirt cheap, it really isn't cost effective to breed and raise one for the showring or pleasure. Nice horses, with good looks, already the color and gender you want, going cheap, cheap , cheap. Between breeding fees, vet checks, foaling out, more healthy mare and foal checks, possible complications before, during, or after the birth, it can be financially and emotionally draining.
I got my gypsy vanner colt as an in utero purchase, I was still on pins and needles, but it was so much more of a relaxing experience. I personally miss having foals, but am so over the worrying aspect of it all (is the mare okay, the foal, healthy delivery or not, enough colostrum, IgG tests, possible colic, possible impactions, weaning, the list goes on ).
Good luck on whatever you choose. Keep an eye on the forum and the sales board in the coming months, you may find something that melts your heart and you can be part of from the beginning, without having to put your own mare at risk.