Like fill-template, except that it does not fill rests. Makes it possible to take the fill symbols from a symbol pattern made with pick-symbol or pick-drum. As a result, the function creates a new symbol pattern based on the rhythm of one pattern, and the symbols of another pattern.
(fill-template-except '(a b (a b c) d e = g) 'a)
--> (a a a a a = a)
(fill-template-except '(a b (a b c) d e = g) '(a = b))