The authority may undertake a project for two or more institutions jointly or for any combination of institutions, and may combine for financing purposes, with the consent of all of the institutions which are involved, the project and some or all future projects of any institution or institutions, and this subchapter applies to and is for the benefit of the authority and the joint participants. However, the money set aside in a fund or funds pledged for any series or issue of obligations shall be held for the sole benefit of the series or issue separate and apart from money pledged for another series or issue of obligations of the authority. To facilitate the combining of projects, obligations may be issued in series under one or more resolutions or trust agreements and may be fully open-ended, thus providing for the unlimited issuance of additional series, or partially open-ended, limited as to additional series. The authority may permit an institution to substitute one or more projects of equal value, as determined by an independent appraiser satisfactory to the authority, for a project financed under this subchapter on terms and subject to conditions the authority prescribes.