Agreed. I had thought about the custom function in the expression language. The only issue I have with that one is that it is also, if ever so slightly, non-intuitive that you change behavior of the entire mapping operation for that row with a function in the expression (which typically just manipulates what data gets assigned).
If you really wanted to be able to set different policies for each row in the mapping table, you could add some sort of per-row setting which would clutter up the UI but might be a little more intuitive. For example, you could set the behavior at the mapper level and then override a particular row with the per-row setting…
Anyway, I will leave it to you to decide how you want to surface the functionality. I am just happy that you see the need for this.
