Overriding package javascript that affects the DOM

I’m using a package that uses javascript to assign a DOM element a width of 240px. If I select the element in template.rendered and give it another width, my code runs after the package’s code, and the size change is visible (it jumps from one size to the other on page load). I’m curious whether there’s a way I can override the package code in my app.

I assume one way is to fork the package and install it as a local package, but then updating will be a problem…