Is it possible to change the source video of a project with another video which is the exact same video (same fps, same aspect ratio, same duration), but with a better resolution, where all the edits on the last source video will remain on the new source video?
My situation is that I've found a 720p version of the 480p video I have been working (a long time) with.
Close Premiere Pro. Rename the old file, then open Premiere Pro. It will ask you where the video file is. Point it to the new version.
As Jim said, you can do this externally.
We sometimes run with proxy media and have that in the Proxy folder with the full quality in the Native (or ProRes) folder. You can either swap the folder names, move the files or in Premiere Pro you can take files OFFLINE then take the online again by right clicking and chosing reconnect media.
That's the easy part
If you've been editing on a 480p timeline then bringing in 720p footage means you either have to change the sequence settings (you could also create a new sequence with the right settings then copy/paste) or you need to tell Premiere Pro to scale your 720p footage down to the 480p sequence size.