As per your message, the foregoing question was submitted to His Eminence, Ayatollah Mahdi Hadavi Tehrani (may Allah grant him long life) and the answer which he gave to the question is as follows:
1. Khums should be spent by the guardian of Muslims' affairs (wali amr) directly or by his authorized representative. Therefore, a person can use Khums or dispose of it only if he has permission from the Wali Amr?
2. A qualified Mujtahid who meets all conditions of Taqlid has Wilayah (guardianship). Hence, one can give his Khums dues to him or his representative irrespective of whether he is his Marja' Taqlid or not. Of course, in the case of the establishment of an Islamic government, the precaution is to give the Khums to him or his wakil (representative). If he consents that Khums be give to any qualified jurists, there would be no objection.
For further information in this regard, refer to the following indexes:
1. Index: Payment of Khums and Permission of Maraje', question No. 690 (site: 737)
Link to Isteftaat Website (code: 176)