Resident abroad when returning quietly stopping taxes mostly (5)
I believe the answer is:
expat
'resident abroad' is the definition.
(I've seen this before)
'returning quietly stopping taxes mostly' is the wordplay.
'returning' is a reversal indicator.
'quietly' becomes 'p' (musical symbol).
'stopping' indicates putting letters inside (stopping can mean blocking a gap).
'mostly' means to remove the last letter (most but not all of the word).
'taxes' with its final letter taken away is 'taxe'.
'p' going within 'taxe' is 'tapxe'.
'tapxe' back-to-front is 'EXPAT'.
'when' is the link.
(Other definitions for expat that I've seen before include "one working abroad" , "Brit abroad, say" , "one settled abroad" , "Person living permanent in a foreign country" , "who now uses overseas address?" .)