Twigs they’re not real hair (8)

'twigs' is the definition.
The definition and answer can be both related to change as well as being verbs in their -s form.
Maybe you can see an association between them that I can't see?

'not real hair' is the wordplay.
I cannot quite see how this works, but
'real' could be 'e' (e is a kind of real) and 'e' is found within the answer.
'hair' could be 'switch' (switch is a kind of hair) and 'switch' is found within the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...

'they're' is the link.

Can you help me to learn more?