I very rarely consider designs as being “done”. Shipping a design is just the beginning of a journey of user testing, quality assurance, and product iteration.
One of the steps in that cycle is working in the design-to-development loop to make revisions to designs.
Whenever possible I like to ship these changes via CSS markup over the final development version.
It helps clearly explain the changes (and avoid miscommunication), as well as making sure that everything in the final product is pixel-perfect.
The easiest possible way to persist these changes is using Stylish.
It’s a small Chrome extension that sideloads a CSS file with your changes.
You can then export the changes and make your customers and developers happier.