Modification to Increase KT Value greater than 50%

Nope.

If there is such a policy it is probably in an agency supplement. NFAS policy for instance states; "Level III contracting officer approval is required when the price of a modification will exceed the original contract price or when the sum of the modifications issued to date, together with the one proposed, exceeds the original contract price."

I do not know of any regulation to that effect, but agree with TAP that if one exists it will be in an agency FAR supplement or some other acquisition policy pronouncement. I can tell you that changes that have increased the cost of the contract by as much as 170 percent have been found to be within the scope of the contract. See Nash & Feldman, Government Contract Changes 3d, sec. 4.5.