The page I linked to also states:
"The Texas Attorney General
has statutory authority to (1) investigate charities that operate as nonprofit corporations, and (2) inspect the books and records of all corporations, including nonprofit corporations."
It sounds like the corporation has been hijacked by those two.
I believe it would be appropriate to raise this problem with the AG. That would not require you to hire a private attorney to gain access to the books and records, and I believe the AG will determine that a lifetime member is still a member despite subsequent amendments to the by-laws.
Complaining to the AG would be a good first step.
on non-profit by-laws states:
Sec. 22.102. BYLAWS. (a) The initial bylaws of a corporation shall be adopted by the corporation's board of directors or, if the management of the corporation is vested in the corporation's members, by the members.
(b) The bylaws may contain provisions for the regulation and management of the affairs of the corporation that are consistent with law and the certificate of formation.
(c) The board of directors may amend or repeal the bylaws, or adopt new bylaws, unless:
(1) this chapter or the corporation's certificate of formation wholly or partly reserves the power exclusively to the corporation's members;
(2) the management of the corporation is vested in the corporation's members; or
(3) in amending, repealing, or adopting a bylaw, the members expressly provide that the board of directors may not amend or repeal the bylaw.
I do not know what the Certificate of Formation says about this, but you should be able to get a copy of the Certificate from the Texas Secretary of State
if you do not have a copy.
I hope this information is helpful.