I believe that along with typing out your message for what troops you would like to the troop icon screen should pop up (the one when donating). You can check the troops you would allow on or off so you don't get any other troops.
You can also set how many of the troop you would like in your clan castle (default is any amount when you click on or off to avoid too much complication)
this will also be able to be changed after the message is sent incase of a mistake or a change of mind.
This will also be used for war castles.
This would have a little green square next to your donation message when your finished typing, and the same for when its in the clan chat.
I feel this would be a useful and simple feature to prevent trolling and mistakes while donations
