It will alter the ratio of BCAA per serving, mixing two different products, one flavored and one unflavored (and probably different ratio's as well as the flavoring)....as long as you are OK with not knowing EXACTLY how many BCAA you are taking in per serving...then no problem. you could always weigh each one, then mix them together, find out the combined mixed weight, and then divide by your scoop size to get an estimate on how many BCAA per serving
I'd do that. mixing 16 oz of bulk 8:1:1 with 8 oz of flavored 4:1:1 for example, you just do the math by weight and the serving scoop size.