Dressing before shaving (9)

I believe the answer is:

preparing

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'dressing' is the definition.
The answer and definition can be both related to change as well as being present participle verbs.
Perhaps they are linked in a way I don't understand?

'before shaving' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'shaving' becomes 'paring' (I've seen this before).
'pre'+'paring'='PREPARING'

Can you help me to learn more?

(Other definitions for preparing that I've seen before include "1 Making ready" , "Making ready (9)" .)

I've seen this clue in The Telegraph.

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