Tax-free scheme's ending to replace agreement (6)
I believe the answer is:
novate
'agreement' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'tax-free scheme's ending to replace' is the wordplay.
'tax-free' becomes 'O VAT' (resembles 0 VAT, zero value-added tax).
'ending' indicates one should take the final letters (the ending of the word).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'replace' becomes 'n' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The final letter of 'scheme' is 'e'.
'ovat'+'e'='ovate'
'ovate' after 'n' is 'NOVATE'.
Can you help me to learn more?
(Another definition for novate that I've seen is " pioneer".)