LP Bylaw Article 13: The rules contained in the current edition of Robert's Rules of Order, Newly Revised shall govern the Party in all cases to which they are applicable and in which they are not inconsistent with other rules adopted by the Party.
LP Bylaw Article 11.7.4: Ranked alternates may be named by the appointing bodies to fill any vacancies in the Convention Committees.
LP Convention Rule 2.3: Duly selected alternates may be freely substituted for any members of their delegation who are temporarily or permanently absent from the floor, provided the procedure has been clearly specified by the affiliate party in advance of the Convention, and the Secretary has been provided with lists of the affiliate party's delegates and alternates as well as a copy of the affiliate party's rules governing substitutions.
RONR p. 571, lines 24-35: If the bylaws authorize certain things specifically, other things of the same class are thereby prohibited. There is a presumption that nothing has been placed in the bylaws without some reason for it. There can be no valid reason for authorizing certain things to be done that can clearly be done without the authorization of the bylaws, unless the intent is to specify the things of the same class that may be done, all others being prohibited.
RONR p. 17, lines 4-18: In some organizations a particular practice may sometimes come to be followed as a matter of established custom so that it is treated practically as if it were prescribed by a rule of order. However, if such a practice is or becomes in conflict with the parliamentary authority or any written rule of the organization, and a Point of Order citing the conflict is raised at any time, the custom falls to the ground, and the conflicting provision in the parliamentary authority or written rule must thereafter be complied with, unless a special rule of order (or, in appropriate circumstances, a standing rule) is added or amended to incorporate the custom. If there is no contrary provision in the parliamentary authority or written rules, the established custom should be adhered to unless the assembly, by a majority vote, agrees to do otherwise.
RONR, p. 483, lines 23-28: Committees of organized societies operate under any applicable rules stated in the bylaws, the special rules of order, the parliamentary authority, and standing rules adopted by the society. Committees may not adopt their own rules except as authorized in the bylaws or in instructions given to the committee by the society.
RONR, p. 469, lines 11-16: In an organized society the board operates under the bylaws, the parliamentary authority, and any applicable special rules of order or standing rules of the society, except as the bylaws may authorize the board to adopt its own rules.
LP Bylaw Article 8.1: The National Committee shall adopt rules of procedure for the conduct of its meetings and the carrying out of its duties and responsibilities.
LNC Policy Manual (Aug 2005) I.2.D: Free substitution of Alternates for Regional Representatives at LNC meetings is permitted.
Either the Party of Principle follows the rules it has voluntarily adopted, or it doesn't.