The review process is an ongoing part of comic creation. Refining visuals based of the current status of the story flow is an essential part of being a good visual story teller. I personally recommend getting most of your illustration corrections done early on so you don’t need to waste a lot of time going over the same panel or page.
In our latest issue of The Scars or Seven, a dialogue change saw the need to add an additional panel. This Correction occurred on page 9. A trick we use when making new panels is first laying out the boundaries of the new panel on top of the original art. When happy with the size and that there won’t be disruption to the existing dialogue bubbles, we draw those boundaries on a new piece of paper. We normally extend the boundary of the new panel on all sides. By drawing the replacement panel the slightly larger than its planned size (or replacement of another panel) you give yourself room draw with more freedom and also you can play with the final placement to get a better look/feel on the final page.
After the panels/pages are penciled, scanned and then checked by inserting it onto their spots in the comic. We then read through the comic, start to finish, and adjust before inking and colouring.