Let's go straight to the MFT docs -
Now to the creation of the callout definition file -
The details here surface in the MFT console - i.e. the MFT user will be
able to add a pre-processing action - "Eire to Ireland text conversion"
Create a simple MFT Transfer to leverage the callout
Now I create a new source (File) in MFT and add a pre-processing step -