I'm a bit interested in this but I'm not sure what problem this is supposed to solve. Doesn't manipulating station priorities do this?
Maybe you're rolling with mixed trains and want to drop off the item which the train has most of first?
Are you wanting a station that receives mixed items call for ...

I used to use an alternative keyboard layout driven by software (ie, installing the keyboard layout on Windows). Wube is amazing, and the hotkeys in Factorio would automatically adjust to conform to the keyboard layout in use.

However, I've now switched to a QMK powered keyboard, where layouts are ...