Journalist, left outside, changed plans (10)

'changed plans' is the definition.
Although both the answer and definition are past participle verbs, I cannot see how they can define each other.

'journalist left outside' is the wordplay.
'journalist' becomes 'ed' (short for editor).
'left' becomes 'resigned' (I've seen this before).
'outside' means one lot of letters goes inside another (some letters go outside others).
'ed' put inside 'resigned' is 'REDESIGNED'.

Can you help me to learn more?