Except as otherwise provided in subsection (b) or elsewhere in [the Uniform Commercial Code], the effect of provisions of [the Uniform Commercial Code] may be varied by agreement.
The obligations of good faith, diligence, reasonableness, and care prescribed by [the Uniform Commercial Code] may not be disclaimed by agreement. The parties, by agreement, may determine the standards by which the performance of those obligations is to be measured if those standards are not manifestly unreasonable. Whenever [the Uniform Commercial Code] requires an action to be taken within a reasonable time, a time that is not manifestly unreasonable may be fixed by agreement.
The presence in certain provisions of [the Uniform Commercial Code] of the phrase "unless otherwise agreed", or words of similar import, does not imply that the effect of other provisions may not be varied by agreement under this section.