These are the basic steps for adding a custom function to the Import-O-Matic API. You will have to pardon my 1992 graphic design :)
1. In the Virtual Fields tab (1) click Launch Code Editor (2)
2. In the Code Editor place your cursor as shown at (1) below and then click the Add Virtual Column button (2)
3. You should now have the highlighted section of code added to your profile
4. Rename the function to whatever you want to call it (1) and add your custom code as in the example at (2) below.
I have added some comments to explain the available variables in the custom function.
5) Then save & close and you are all set!
You should now see the name of your custom function show up in the drop down when you click on the custom function column in the IOM profile.