The most common and most likely answer to this crossword clue is the 9 letter word OPERATORS
O
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A
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More clues leading to the result OPERATORS
Buddy explains!

The straight part
We know that "Employees in exchanges, or in certain theatres?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case employees in exchanges, or in certain theatres? = operators.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.
What does OPERATORS mean?
OPERATORS noun- One who operates.
- A telecommunications facilitator whose job is to establish temporary network connections.
- A function or other mapping that carries variables defined on a domain into another variable or set of variables in a defined range.
- The game of Chinese whispers.
- A person who is adept at making deals or getting results, especially one who uses questionable methods.
- A member of a military special operations unit.
- The administrator of a channel or network on IRC.
- A symbol that represents a construct in a programming language and differs from a normal function in its syntax.
- A kind of expression that enters into an a-bar movement dependency and is said to bind a variable.