Frenchman swapping roles a bit (6)
I believe the answer is:
morsel
'a bit' is the definition.
(I know that bit can be written as morsel)
'frenchman swapping roles' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'swapping' is an anagram indicator (I've seen 'swaps' mean this).
'roles' with letters rearranged gives 'orsel'.
'm'+'orsel'='MORSEL'
(Other definitions for morsel that I've seen before include "Tidbit" , "A tiny bit" , "Small amount of food, a bite" , "Titbit" , "A small amount of food, just a piece" .)