Hi all,
wanting to modify the CSS of a core module (JqueryMagnific in my case), but not to touch the files in \wire\, I found this older blog entry:
https://processwire.com/blog/posts/processwire-core-updates-2.5.14/#multiple-copies-of-the-same-module
That might be helpful for others, too.
(It's pure fun using PW!)