It's time for a small update. If you go to one of your recipes, click the blue wrench and click "Adjust total flavor %".
It does exactly that - Adjusts the total flavor percentage, keeping the ratio. Now it's not the most elegant solution, using a browser prompt for the input - but this has been on my list in forever, so I just wanted something quick that worked
I hope you'll find it useful!
EDIT 2016-11-30: Adjust total flavor % now edits instead of adapting.