(a) Except as otherwise provided in Subsection (b) or elsewhere in this title, the effect of provisions of this title may be varied by agreement.
(b) The obligations of good faith, diligence, reasonableness, and care prescribed by this title 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 this title requires an action to be taken within a reasonable time, a time that is not manifestly unreasonable may be fixed by agreement.
(c) The presence in certain provisions of this title 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.