On written request by a federal agency operating a federal witness security program established under 18 U.S.C. 3521, the registration requirement for a sex offender under the protection of a federal witness security program is waived and the person under protection is exempt from registration. On written request by a nonfederal agency that operates a witness protection program comparable to a federal program established under 18 U.S.C. 3521, the registration requirement for a sex offender under the protection of a witness protection program is waived and the person under protection is exempt from registration. A waiver granted under this section is terminated, and registration is required, if a sex offender exempted from registration under this section subsequently is convicted of an offense that requires registration under this subtitle.