(a) Imposed duties to control. If any provision of the indenture to be qualified limits, qualifies, or conflicts with the duties imposed by operation of subsection (c) of this section, the imposed duties shall control.
(b) Additional provisions. The indenture to be qualified may contain, in addition to provisions specifically authorized under this subchapter to be included therein, any other provisions the inclusion of which is not in contravention of any provision of this subchapter.
(c) Provisions governing qualified indentures. The provisions of sections 310 to and including 317 of this title that impose duties on any person (including provisions automatically deemed included in an indenture unless the indenture provides that such provisions are excluded) are a part of and govern every qualified indenture, whether or not physically contained therein, shall be deemed retroactively to govern each indenture heretofore qualified, and prospectively to govern each indenture hereafter qualified under this subchapter and shall be deemed retroactively to amend and supersede inconsistent provisions in each such indenture heretofore qualified. The foregoing provisions of this subsection shall not be deemed to effect the inclusion (by retroactive amendment or otherwise) in the text of any indenture heretofore qualified of any of the optional provisions contemplated by section 310(b)(1), 311(b), 314(d), 315(a), 315(b), 315(d), 315(e), or 316(a)(1) of this title.