The most common and most likely answer to this crossword clue is the 10 letter word WIG-MAKERS
I've seen this crossword clue in The Guardian
W
I
G
-
M
A
K
E
R
S
Buddy explains!
The straight part
We know that "Those responsible for changing locks in the theatre?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case those responsible for changing locks in the theatre? = wig-makers.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.