New York state education officials are proposing to eliminate a series of less-rigorous exams used for students with disabilities to earn high-school diplomas. Under the proposal, students with disabilities would have three ways to earn a local diploma, a lesser diploma no longer available to those without disabilities who must earn a Regents certificate. The state also is proposing several new diplomas and a Skills and Achievement Commencement Credential, designed to replace the I.E.P. diploma, which is not accepted by colleges or the military.