This is tricky, because the version of Samba I need ist no longer available on the Repos.

Remove the software you want to downgrade:

rpm -qa | grep samba | xargs rpm -e --nodeps
rpm -e --nodeps libsmbclient libwbclient

Manually install the needed Version:

[root@backup x86_64]# ls -1
libsmbclient-4.1.1-10031.el7.centos.x86_64.rpm
libwbclient-4.1.1-10031.el7.centos.x86_64.rpm
samba-4.1.1-10031.el7.centos.x86_64.rpm
samba-client-4.1.1-10031.el7.centos.x86_64.rpm
samba-common-4.1.1-10031.el7.centos.x86_64.rpm
samba-dc-4.1.1-10031.el7.centos.x86_64.rpm
samba-dc-libs-4.1.1-10031.el7.centos.x86_64.rpm
samba-libs-4.1.1-10031.el7.centos.x86_64.rpm
samba-pidl-4.1.1-10031.el7.centos.x86_64.rpm
samba-python-4.1.1-10031.el7.centos.x86_64.rpm
samba-test-4.1.1-10031.el7.centos.x86_64.rpm
samba-vfs-glusterfs-4.1.1-10031.el7.centos.x86_64.rpm
samba-winbind-4.1.1-10031.el7.centos.x86_64.rpm
samba-winbind-clients-4.1.1-10031.el7.centos.x86_64.rpm
samba-winbind-krb5-locator-4.1.1-10031.el7.centos.x86_64.rpm
samba-winbind-modules-4.1.1-10031.el7.centos.x86_64.rpm

yum install *.rpm

Check if all deps are solved:

yum check

Pin the needed package versions:

yum -y install yum-versionlock
yum versionlock add samba\* BackupPC

 

Exclude the Versions from beeing upgraded:

vi /etc/yum.conf
------
[main]
...
exclude=*samba* libsmb* libwbclient* BackupPC
------

 

Check if yum is doing as expected:

yum makecache
yum upgrade