Neat, so you are running both bootstrap and your custom css file and js file in parallel on your app? How are you guys quantifying what parts to work on?
Typically it takes just a few minutes to switch out the CSS.
Now, there are a few very complex screens that require more effort (a lot of data viz and variable state). Those we evaluate - maybe we will punt on the upgrade – or maybe we dig in and do it if there is nothing urgent on the books.