Mahzorim  receive qualifiers if  they  are "authorized or  traditional variant(s) or special text(s)  of  a liturgical work"
(rule 25.22A).  The first numbered section of  the rule specifies  that the qualifier may  be  the  name  of  a special "rite,"
e.g.  "Haggadah (Sephardic)" or, as we see later in the rule, "Haggadah  (Reform)."
 
After the numbered sections, the rule goes on, "If  a single  term  is insufficient to identify the variant text, add  a second
term (e.g., the name of the editor)," with the examples "Haggadah  (Reform, Guggenheim)" and "Haggadah, (Reform, Seligmann)."

So these are the headings for variant texts.
 
If what you're cataloging is only a *part* of such a variant text, then the name of the part follows the qualified heading for
the text as  a  $p.  It's the text that's qualified, not the part of  the  text,  thus "Mahzor (Reform, Temple  Emet,  Los Angeles,
Calif.).$pHigh  Holidays."   (Note   that,  similarly,  corporate bodies  are qualified, but  not  $b  sub-bodies except  in  weird
circumstances.)  For  an example of something like this qualified by   a  corporate  body,   see  "Catholic  Church.  Missal   (St.
Augustine's Abbey, Canterbury, England)" near the top of  p. 515, and note the punctuation.