Pretty soprano replaces tenor? That's more imprudent (6)
I believe the answer is:
rasher
'more imprudent' is the definition.
('rash' can be similar in meaning to 'imprudent')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for rasher that I've seen before include "taking more unnecessary risks?" , "eat this?" , "Tasty strip of bacon" , "type of food" , "bit of a pig" .)