Troops invading England's boundaries? Correct (5)
I believe the answer is:
emend
'correct' is the definition.
(thesaurus)
'troops invading england's boundaries?' is the wordplay.
'troops' becomes 'men' (I've seen this in other clues**).
'invading' is an insertion indicator.
'boundaries?' suggests removing the centre (only the edge or boundary letters remain).
'england' with its middle taken out is 'ed'.
'men' inserted into 'ed' is 'EMEND'.
(Other definitions for emend that I've seen before include "Polish" , "Make improvements to (text)" , "make an improvement" , "Make improvements or corrections" , "would appear better" .)