I was just looking for the answer to this question too so I found this thread only to discover no answers yet
But then I figured it out!!
Click on the recipe you want to adjust (not the edit option, just the actual recipe name) then click the orange writing saying "create a recipe makeover" it's the second option underneath the nutrition info box, and the recipe pops up with the ingredient list able to be changed as you want. I imagine this should work with other people's recipes too although I haven't tried.
I think this is the solution - let me know if it works for you.