ok the mission settings UI has been completed:
Here's how it works:
when you click on a mission it gathers all the information it needs from the mission's files. It updates the mission settings box but the box isn't visible yet. Once you mouse into 'Start' the mission settings box appears for you to make any changes you want. When you're finished with the changes you click 'Apply changes'. Then click 'Start' and enjoy your changed mission.
If you click on another mission or mouse into 'Back' the mission settings box will hide.
You click on the value of the entry to change it. Those that require keyboard entry will display an edit box for you to type a value into. Those that don't require use entry will scroll through available values with each click on the value.