You need rebase instead.

Yep yep, that’s what I do for my feature branches! ;)
Or, well, at least when I’m the only one working on them, anyway~

when it comes time to PR

Oh haha, I really doubt I need to worry about that; these are pretty community-specific features, I doubt the upstream project would even want them. I am concerned only with keeping my fork’s main development branch up to date with the upstream’s. Y’know, after I merge my custom features into it. There seem to be a bunch of intricate ways to do it (see the blogpost I linked), and I’m unsure if I should care about any of those, or if I can get away with just, doing a normal merge.

Oh, no, haha, I didn’t mean merging my changes into upstream! I meant merging upstream changes into my fork :p
edit: changed wording in my post so it’s a bit more clear what I mean~