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Typically the Operating Agreement for an LLC will specify how owner members (partners or principals) can be added to the LLC. The Operating Agreement would typically provide for managers of the LLC or election of officers of the LLC as well.
If your current Operating Agreement does not provide for those additions you do not necessarily need to amend the Operating Agreement as the law, Title 6, Chapter 18 of the Delaware Code, provides for the admission or addition of member owners of the LLC.
Section 18-301 of the Delaware Code provides that after the formation of a Limited LIability Company a person may be admitted upon the consent of all members.</p.
Please see the public domain link to the Delaware Code provided below:
The member owners could then also elect the individual to an officer position as CIO.
If you prefer to also amend the Operating Agreement of the LLC to specifically provide for the admission of new members, the Operating Agreement may be amended by following the provisions in the Operating Agreement to amend it.
Following is a direct link to public domain sample operating agreements for a Delaware LLC. It includes language in Article II of the sample as to the admission of new members.
I hope this information is helpful and responsive. If you would like further clarification, please let me know.