Hmm, rpm-ostree doesn’t seem to handle dependencies when replacing packages.
[jlh@citrus ~]$ rpm-ostree override replace https://kojipkgs.fedoraproject.org//packages/kernel/5.1.9/300.fc30/x86_64/kernel-5.1.9-300.fc30.x86_64.rpm
Downloading 'https://kojipkgs.fedoraproject.org//packages/kernel/5.1.9/300.fc30/x86_64/kernel-5.1.9-300.fc30.x86_64.rpm'... done!
Checking out tree d57cc45... done
Enabled rpm-md repositories: enpass fedora updates
rpm-md repo 'enpass' (cached); generated: 2019-05-29T05:51:52Z
rpm-md repo 'fedora' (cached); generated: 2019-04-25T23:49:41Z
rpm-md repo 'updates' (cached); generated: 2019-06-23T01:10:10Z
Importing rpm-md... done
Resolving dependencies... done
error: Could not depsolve transaction; 1 problem detected:
Problem: conflicting requests
- nothing provides kernel-core-uname-r = 5.1.9-300.fc30.x86_64 needed by kernel-5.1.9-300.fc30.x86_64
- nothing provides kernel-modules-uname-r = 5.1.9-300.fc30.x86_64 needed by kernel-5.1.9-300.fc30.x86_64
[jlh@citrus ~]$
I tried doing the command with the packages for kernel-core and kernel-modules added too, but that just gives the same error.