In the United States, administrative authorities do not have the ability to independently decide to grant or withhold a prisoners' rights which are set by case, statute, and constitutional law. The restriction of rights must be done under the limitations of law and not at the arbitrary discretion or whim of an executive authority.
In regard to special meals, hair length, and style, prayer times, and clothing, rights can be restricted or limited if a reasonable evaluation determines that the prisoner does not exhibit a "sincerely held belief" in the religion he or she professes that would necessitate some accommodation (see Vaughn v. Garrison). In imposing restrictions that interfere with religious beliefs, the prison administrator must apply the restriction neutrally and equally upon all prisoners, and not single out a specific practice (see Oregon v. Smith).
The case of hair length and style, however, has been the subject of specific scrutiny. In Hines v. South Carolina and other cases, the Supreme Court determined that hair length and style is almost invariably a matter of prison security and have granted administrators widespread discretion to establish and enforce grooming standards, subject to the neutral rule requirements of Oregon v. Smith.
In terms of meals, a prisoner has an absolute right to avoid eating certain foods that conflict with his or her religious beliefs and this right generally cannot be restrained by a prison official. Whether or not a prisoner can demand service of certain foods is a different question. The courts have generally held that such demands can be made, provided it is not unreasonable for the prison to make such provisions. So, for instance, a prisoner who demanded to eat lion meat as part of a religious belief could be denied that request, even if it were determined this was a belief that was "sincerely held" since the acquisition of lion meat by a prison kitchen would be difficult and unreasonable.