Automatic translation/version between American and English

Does anyone know of an add-on to MS Word that can do an automatic translation or conversion from American to English or vice versa? – ie English (UK) to English (USA)

Most of us know how to set the language to English (UK) and then run the spell checker, but surely someone has come up with a bit of software to do this in a more automated way.

I imagine a list of word pairs (e.g. color-colour, instill-instil, etc) that can be customised (customized…) as desired and then set to run automatically through a document in one go.

Any ideas?