Plan to put diplomacy in charge (6)
I believe the answer is:
tactic
'plan' is the definition.
(tactic is a kind of plan)
'diplomacy in charge' is the wordplay.
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'tact'+'ic'='TACTIC'
'to put' acts as a link.
(Other definitions for tactic that I've seen before include "Scheme or ploy used in battle, sport, etc, often within an overall strategy" , "Manoeuvre, stratagem" , "Military manoeuvre" , "Military means to an end" , "Planned manoeuvre or skilful move" .)