Have you ever found yourself wanting to merge references, and then found it tedious to find and replace all the reuses of that reference? What you need may just be a script called RefMan (for Reference Manager), which allows you to drag and drop references into each other to merge them. You may also update and delete references. It is similar to ProveIt, however, there are some important differences:

ProveIt tries to understand the actual content inside <ref> tags, and parses {{cite}} templates and such. RefMan makes no attempt to understand, apart from finding the URLs.
RefMan was developed for me, by me. It uses ES6 Javascript features, and makes some presumptions about the user's wikipedia settings. For the best result, be me. If that is not an option, you could try using a modern version of Firefox, which is what I use.
RefMan knows exactly where references are located in the main text at all times. ProveIt at this moment (April 2017; ProveIt is actively being developed) does not have the same grip on that information, so, for example, ProveIt can't deal with two identical <ref> tags. It will find them both, but if you try to edit the second one, it will change the first one. RefMan works very differently in that regard, it makes no such guesses. RefMan is like an all-seeing eye. If you get my drift.
When you change the location of the cursor in the wikitext so that it is inside a <ref> tag, RefMan highlights which reference that is in RefMan's interface, making it easy to switch between editing the wikitext and using the RefMan interface.
For more features or details, read the source (RefMan is licensed under the GNU GPLv3, and is therefore Free software)
To install, follow these instructions, using {{subst:iusc|User:Uglemat/RefMan.js}}
After you have installed, there should appear a button with the totally cool RefMan logo in the editing toolbar, which toggles the RefMan interface.

Usage: