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For your information- A codicil is a document to make an alteration to an existing Will, as opposed to an Enduring Power of Attorney (EPA).
EPA's are no longer used, and have been replaced by Lasting Powers of Attorney. Any existing EPA is still valid so don't panic. However, it is not possible for you to make any amendment to an existing EPA.
If you do wish to change who your Attorneys are, you would have to destroy the EPA and get a Lasting Power of Attorney drawn up.
I hope this assists and sets out the legal position.