A presenter at home cutting unusually large borders (7)
I believe the answer is:
adjoins
'borders' is the definition.
('adjoin' can be a synonym of 'border')
'a presenter at home cutting unusually large' is the wordplay.
'presenter' becomes 'dj' (radio DJ).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'cutting' indicates putting letters inside (some letters cut their way into a word).
'unusually large' becomes 'OS' (short for over-size).
'in' inserted within 'os' is 'oins'.
'a'+'dj'+'oins'='ADJOINS'
(Another definition for adjoins that I've seen is " Lies adjacent to".)