Most of Rheingold arranged with new, alternative opera name (9)
I believe the answer is:
lohengrin
'opera name' is the definition.
(Lohengrin is a Wagner opera)
'most of rheingold arranged with new' is the wordplay.
'most of' means to remove the last letter.
'arranged with' indicates an anagram.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'rheingold' with its last letter removed is 'rheingol'.
'rheingol' mixed up with 'n' can make 'LOHENGRIN'.
'alternative' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
(Other definitions for lohengrin that I've seen before include "Musical entertainment" , "Wagnerian opera" , "Wagner opera" .)