Hand in notice, besieging editor for new plan (8)
I believe the answer is:
redesign
'new plan' is the definition.
(I've seen this before)
'hand in notice besieging editor' is the wordplay.
'hand in notice' becomes 'resign' (to hand in one's notice is to resign).
'besieging' means one lot of letters goes inside another.
'editor' becomes 'ed'.
'resign' going around 'ed' is 'REDESIGN'.
'for' acts as a link.
(Other definitions for redesign that I've seen before include "New look" , "Make new plans" , "Plan again differently" , "Modernise" , "Plan something again" .)