Tl;dr : I'd like to find an app that switches any part of an url with a certain pattern to another chosen pattern when I open it.

Explanation of what I'm trying to do:

An institution I have an account in offers free access to a few online publications that are normally behind a paywall, via ezproxy. The standard way to use it is impractical: You must go through the institution's website, log on, go to the page listing online ressources, find the one you're looking for and log in to your account to access it. What's more, the rss feeds of the proxy version of these sites don't work.

A quicker way to access it is to go on the (paywalled) article, switch a part of the url with a certain pattern that's always the same, and log in if not already done. On my desktop, I could use a Firefox addon named "redirector" to do this automatically. This way, I follow the publications normal website rss feed, and when I click on the link I get the unpaywalled version. But I also look a feeds on my phone, with Feeder, and I'd also like being able to get the full articles there (I don't mind opening the article in a brower). Firefox for Android and it's forks don't have the Redirector add-on tho. Is there another way I could do the same thing on Android, so I can click on a feed and have it redirect to the proxy version?

Ideally, I'd like the solution to be FOSS.

(My phone isn't rooted and cannot be, as the bootloader is locked)