Sweet and spicy BBQ venison snack sticks??

Yes, you can "alter" or amend any store bought spice mix as you like.  I've modified the flavor profile of store bought several times when I, like you, thought it needed a little something extra.  Adding BBQ sauce or other spices should not alter the amount of cure needed either.  That only changes if you use more meat.

I often take crushed red pepper (think pizza pepper) and run it through my spice grinder to make it a little finer (but not to the point of becoming a powder).  That adds some spice with flavor as opposed to just heat like adding cayenne (but, I guess it depends on how much of a pepper head you are as to what you add).  For extra sweet, try adding honey. 

Not sure I'd add BBQ sauce to a premixed spice mix.

If you do start with a small batch like 1 pound. That way you aren't wasting a large quantity of meat.

If you like the outcome adjust the amount for larger quantities.