The Compile function can transform smart quotes to straight for you when it creates your output. So, you will never need to actually change this back in your Scriv documents.
Compile > Summary
or for more fine grained control:
Compile > All Options > Transformations
It is a wonderful feature of Scrivener that it gives you a great deal of latitude in setting up your work environment, because it is built with the understanding that how you want things to be set up for writing is not the same thing as how something must look in your final output.
And Scrivenings group mode is more than awesome.
Best,
gr