use older repo to install older program

edit

Well I was able to make a repo that pointed to the old Fedora25. I had a backup copy of 25's /etc/yum.repos.d/fedora.repo. So I took the "fedora" repo from that and put it in a new repo file called "fedora_archives.repo":

[fedora25]
# $releasever=25
# $basearch=x86_64
name=Fedora 25 - x86_64
failovermethod=priority
baseurl=http://download.fedoraproject.org/pub/fedora/linux/releases/25/Everything/x86_64/os/
metalink=https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64
enabled=1
metadata_expire=7d
repo_gpgcheck=0
type=rpm
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-25-x86_64
skip_if_unavailable=False

Then I tested it with:

~>  dnf  --showduplicates list warzone2100 
Last metadata expiration check: 0:01:59 ago on Wed 28 Nov 2018 06:43:12 PM EST.
Installed Packages
warzone2100.x86_64                     3.2.3-8.fc29                     @fedora 
Available Packages
warzone2100.x86_64                     3.2.1-1.fc25                     fedora25
warzone2100.x86_64                     3.2.3-8.fc29                     @fedora 
warzone2100.x86_64                     3.2.3-8.fc29                     fedora

And then ran:

~>  sudo dnf downgrade warzone2100 3.2.1-1.fc25

And it proceeded normally until dnf asked me to ok a gpg key which I had never been asked before. I don't know much about that but I answered y anyhow. Hope that's ok. Think it's like approving an ssh key for the first time.:

warning: /var/cache/dnf/fedora25-310f9d37d74ceec1/packages/libGLEW-1.13.0-2.fc24.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fdb19c98: NOKEY
Fedora 25 - x86_64                              1.6 kB/s | 1.6 kB     00:01    
Importing GPG key 0xFDB19C98:
 Userid     : "Fedora 25 Primary (25) <fedora-25-primary@fedoraproject.org>"
 Fingerprint: C437 DCCD 558A 66A3 7D6F 4372 4089 D8F2 FDB1 9C98
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-25-x86_64
Is this ok [y/N]: y
Key imported successfully

After that it installed aok. And this version of wz runs real time instead of 1 second per 3 er 4! Have not noticed any difference otherwise.