... contract for plaintiff than the contract plaintiff created for itself. N.J.S.A. 12A:2-209 provides that 'an attempt at modification' of a sales contract ... the 'signed agreement . . . excludes modification . . . except by a signed writing.' N.J.S.A. 12A:2-209(2) to (4); U.C.C. ยง 2-209 cmt ...