Actually, in 1993 - notice the time frame - the Nevada Legislature passed an amendment eliminating the phrase: “[they forever disclaim all right and title to the unappropriated public lands lying within said territory, and that the same shall be and remain at the sole and entire disposition of the United States; and that]”
http://www.leg.state.nv.us/Statutes/67th/Stats1993R01.html#FIz189_zSJRz27
How valid it is to amend the document you entered the Union under, in which you DID “forever disclaim all right and title”, is open to question. Generally speaking, a contract between two parties cannot be changed without the consent of both parties.
Just saw this footnote - the amendment becomes “effective on the date Congress consents to amendment or a legal determination is made that such consent is not necessary.”