I also do a 50/50 mix of guinea pig and chinchilla pellets
. As everyone has said, not all food has molasses in it. Just check the label, and you'll be fine.
It's important, if you do use guinea pig food, not to get one with all the "extras" in it (like little cereal flakes, bits of corn, little puffs, etc.). Stick to a basic, pellet only guinea pig food, as all the little extras are extra bad for Goos.
Mine have free access all day to all the pellets, hay, and water they want. Once a day I also give veggies - the fancy lettuces, peas, green beans, a carrot, sweet potato, dandelion greens
Each time I clean cages, they all get a peanut for a treat, and every now and then I'll give a few sunflower seeds, or something else like that, for an extra special treat.
I know you are going to LOVE having Degus in your life. Congratulations!!!