Replace source clips in media pool?

[Second edit: I'm a dumbass. The processed clips weren't in 16:9 despite them being supposed to be in 16:9. Everything I describe below is most likely working, but to solve my "problem" I added zoom to all clips.]

[Edit: I clarified the problem.]

Hi all.

I've been searching both the Internet on this forum to try and find a conclusive answer for this but it's hard to formulate a good query. :/

I have several clips in 4k 4:3 resolution and ratio that I used to edit a video, with the intent to replace them with the correct clips that are 2.7k and 16:9.

I replace the old clips with the new clips on the file server and try to relink the clips in the media pool, but the clips stay the same in the timeline and the exported video is still in 4:3. I tried to replace the clips in the media pool, one by one, without success.

It occurred to me that I might have to change the project settings for input and output scaling, so I experimented with that without any effect.

I tried the "Conform lock with media pool clip" action and that didn't do anything.

What am I missing or doing wrong?

Thanks.