Any plugin or script for automatically converting US English to UK English?

I am currently working on a project that involves editing over 20 press releases every day. Unfortunately, most of these are in US English while the client’s website uses UK English.
So I am stuck with the rather tedious task of manually changing multiple words (eg, organization to organisation, color to colour) in each press release.
In Scrivener, I have set the dictionary as UK English and so the ‘misspelt’ words get highlighted. Which makes things easier. However, can I take this one step further and automatically ‘correct’ these words? Maybe a script or the equivalent of a macro that I could run? If not in Scrivener, is there any way to do this in MS Word?