Nothing in these regulations may be construed as:

(a) Affecting, modifying, diminishing, or otherwise impairing the sovereign immunity from suit enjoyed by an Indian Tribe;

(b) Authorizing or requiring the termination, waiving, modifying, or reducing of any existing trust responsibility of the United States with respect to the Indian people;

(c) Permitting significant reduction in services to Indian people as a result of this part; or

(d) Mandating an Indian Tribe to request a contract or contracts. Such requests are strictly voluntary.