Change your voting system after revolution (4)
I believe the answer is:
vary
'change' is the definition.
(synonyms)
'your voting system after revolution' is the wordplay.
'your' becomes 'yr'.
'voting system' becomes 'av' (alternative vote electoral system).
'after revolution' is a reversal indicator.
'yr'+'av'='yrav'
'yrav' backwards is 'VARY'.
(Other definitions for vary that I've seen before include "Diversify" , "Differ from a standard" , "Undergo change" , "Fluctuate" , "Be or become diverse" .)