Since CentOS Linux 8 will lose support on December 31, 2021 and the focus will be solely on CentOS Stream 8, which is continuously delivered distro that tracks just ahead of Red Hat Enterprise Linux (RHEL) development, positioned as a midstream between Fedora Linux and RHEL, many are looking for alternatives. Thankfully they exist and there are conversions that I have tested on fresh installs of CentOS Linux 8 to convert to other distributions.
Before beginning, be certain to apply all the operating system updates in advance, otherwise you may encounter odd anomalies like perl conflicts to downgraded packages. At least those were some of the side-effects that was encountered on one test and the only thing that I can attribute is that the OS was a point release behind the converted release.
Rocky Linux 8
This process has been tested successfully several times on development / test machines.
dnf update rpm -e --nodeps centos-gpg-keys centos-linux-release centos-linux-repos rpm -ivh \ https://download.rockylinux.org/pub/rocky/8/BaseOS/x86_64/os/Packages/rocky-release-8.4-23.el8.noarch.rpm \ https://download.rockylinux.org/pub/rocky/8/BaseOS/x86_64/os/Packages/rocky-repos-8.4-23.el8.noarch.rpm \ https://download.rockylinux.org/pub/rocky/8/BaseOS/x86_64/os/Packages/rocky-gpg-keys-8.4-23.el8.noarch.rpm dnf distro-sync -y
On one test machine the above steps worked without any additional steps. However, the following two steps remediated additional things on another machine.
cd /boot rm *rescue*