I'm stealing this idea from Tableau's number formatting, it's a timesaver.
In the DateTime tool if I've initially selected a value besides Custom in the "Select the format..." list then when I click Custom rather than having the Custom textbox be blank I'd like to have it automatically populated with whatever formatting string I just selected. Here's an example screenshot:
![](blob:https://community.alteryx.com/53e280e7-7fc7-444c-bad8-2bf16f1a037b)