If it's loaded with artificial sweeteners adding yeast won't achieve what you're looking for. Cane sugar or high fructose corn syrup will work, though.
Things "loaded" with artificial sweeteners have 1/200th (aspartame) to 1/1000th (sucralose) the quantity of the equivalent sugar. A can of diet coke has 0.2 gm aspartame, while regular coke has 39gm sugar.
Aspartame/sucralose are chemicals, and are of course not fermentable, and they do not put those in John Daly or any other alcoholic beverage that's not listed as low carb, in fact I don't know of a single alcoholic beverage with artificial sweetener in it, with that one that had monk fruit sweetener as well as the stevia sweetened long island ice tea being the closest.
Though stevia and monk fruit are likely edible by microbes IMHO they are not artificial, they are from plants and stevia is about 150 times as sweet as sugar, monk fruit is 300X. I'm sure they are edible by microbes, though they may preferentially feed bacteria over yeast.
I am not adding sugar or corn syrup and yeast to increase the ABV of this sugary concoction, I am adding yeast to replace the sugar already in it because I am a low carb guy. I'm pretty sure its got real sugar, but it also has preservatives, I'm sure, so it would not ferment on that count alone. Lets see.
Now my little encouragement here is - honey. Honey has antiseptic in it, as in, it kills microbes, however its the viscosity that prevents it from getting fermented. Now if you dilute it, it ferments rather easily and makes mead. I used champagne yeast in the John Daly super ferment. Has a distinct taste, so I'll detect it if it is even taking hold.
Cool.
Srinath.