Make significant changes out of boredom (4)
I believe the answer is:
redo
'make significant changes' is the definition.
(to redo is to change or do again)
'out of boredom' is the wordplay.
'out of' says the answer is hidden in the clue.
'REDO' is hidden in the letters of 'boredom'.
(Other definitions for redo that I've seen before include "Redecorate or repeat action" , "further attempt?" , "Create again" , "Make anew" , "Have second thoughts" .)