I googled Humalin Mix 25 and it say Humalog mix 25? It looks like a "mixed" insulin with both novolog and some sort of longer acting stuff mixed in? I think this might cause more challenges than it's worth. I always did the shots separately, although I was using R and N instead of the "fancier" new insulins. I think that it's pretty challenging to balance food and activity with the mixed insulins and that might might the case with the mix 25.
I have lost weight since maybe 2006 pretty much watching carbs. For me, I get my insulin set to where the BG is flat, then sort of review the carbs and cut out what I can and see what happens. So far, at each stage, I've done stuff like going from sandwich + chips@ lunch to sandwich to 1/2 sandwich and, each time I've cut out carbs, it seems as if some weight comes off. It's important to me to try to keep the BG relatively flat.