> there were still some functions and symbols that weren't acknowledged such as "display-musicxml" and "'atonal" (inside a def-score)
I am not a Opusmodus user (Just a Common Lisper) but IMHO, I think there is Common Lisp PACKAGE and SYMBOL related things like a described below link.
If "display-musicxml" and "atonal" symbols are not exported, You may IMPORT them, like
(:use :cl :bordeaux-threads :opusmodus)
(:import-from ??? :display-musicxml :atonal))
If "display-musicxml" and "atonal" symbols are exported, You may USE-PACKAGE, like
(:use :cl :bordeaux-threads :opusmodus ???))
;; How to find the ??? package => (find-all-symbols (string '#:display-musicxml))