Ok, if you have a bow that is pulling 28" or so with a 7 1/2" brace if you add a longer string thus making the brace smaller will you gain draw length?
No. Draw length is measured from the bow, not the string. You may gain a touch of efficiency as the string travel will be longer. But generally, there is not a whole lot of energy stored in the first couple inches of pull.
The longer the string the less the arms bend (less tention on the arms), eventing in a weaker shot. In short, the more tention there is the better the shot.
Shorter string = greater tention
Longer string = less tention