Right to replace 50 among soldiers in sector (6)

I believe the answer is:

region

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'sector' is the definition.
(I know that sector can be written as region)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for region that I've seen before include "Area having definable character" , "Wide area" , "Area - district" , "Tract or area" , "Ignore (anag) - area" .)

I've seen this clue in The Telegraph.

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