Ok the new commands worked perfectly. Thank you very much!
 [root@smeserver-10 ~]# yum downgrade libtevent  --disablerepo=* --enablerepo=sme
updates-testing,smeos,smeupdates
Loaded plugins: fastestmirror, post-transaction-actions, smeserver
Loading mirror speeds from cached hostfile
 * smeos: mirror.canada.pialasse.com
 * smeupdates: mirror.canada.pialasse.com
 * smeupdates-testing: mirror.canada.pialasse.com
Resolving Dependencies
--> Running transaction check
---> Package libtevent.x86_64 0:0.9.28-1.el7 will be a downgrade
---> Package libtevent.x86_64 0:0.9.31-2.el7_4 will be erased
--> Finished Dependency Resolution
Error: Package: python-tevent-0.9.31-2.el7_4.x86_64 (@smeupdates)
           Requires: libtevent(x86-64) = 0.9.31-2.el7_4
           Removing: libtevent-0.9.31-2.el7_4.x86_64 (@smeupdates)
               libtevent(x86-64) = 0.9.31-2.el7_4
           Downgraded By: libtevent-0.9.28-1.el7.x86_64 (smeos)
               libtevent(x86-64) = 0.9.28-1.el7
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest
[root@smeserver-10 ~]# rpm -q libtevent
libtevent-0.9.31-2.el7_4.x86_64
[root@smeserver-10 ~]# yum update smeserver-yum --enablerepo=smeupdates-testing -y
Loaded plugins: fastestmirror, post-transaction-actions, smeserver
Loading mirror speeds from cached hostfile
 * base: mirror.netflash.net
 * smeaddons: mirror.canada.pialasse.com
 * smeextras: mirror.canada.pialasse.com
 * smeos: mirror.canada.pialasse.com
 * smeupdates: mirror.canada.pialasse.com
 * smeupdates-testing: mirror.canada.pialasse.com
 * updates: mirror2.evolution-host.com
No packages marked for update
[root@smeserver-10 ~]# signal-event yum-modify
[root@smeserver-10 ~]# yum downgrade libtevent  python-tevent --disablerepo=* --
enablerepo=smeupdates-testing,smeos,smeupdates
Loaded plugins: fastestmirror, post-transaction-actions, smeserver
Loading mirror speeds from cached hostfile
 * smeos: mirror.canada.pialasse.com
 * smeupdates: mirror.canada.pialasse.com
 * smeupdates-testing: mirror.canada.pialasse.com
Resolving Dependencies
--> Running transaction check
---> Package libtevent.x86_64 0:0.9.28-1.el7 will be a downgrade
---> Package libtevent.x86_64 0:0.9.31-2.el7_4 will be erased
---> Package python-tevent.x86_64 0:0.9.28-1.el7 will be a downgrade
---> Package python-tevent.x86_64 0:0.9.31-2.el7_4 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
 Package               Arch           Version               Repository     Size
================================================================================
Downgrading:
 libtevent             x86_64         0.9.28-1.el7          smeos          34 k
 python-tevent         x86_64         0.9.28-1.el7          smeos          17 k
Transaction Summary
================================================================================
Downgrade  2 Packages
Total download size: 51 k
Is this ok [y/d/N]: y
Downloading packages:
(1/2): libtevent-0.9.28-1.el7.x86_64.rpm                   |  34 kB   00:00
(2/2): python-tevent-0.9.28-1.el7.x86_64.rpm               |  17 kB   00:00
--------------------------------------------------------------------------------
Total                                               91 kB/s |  51 kB  00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : libtevent-0.9.28-1.el7.x86_64                                1/4
  Installing : python-tevent-0.9.28-1.el7.x86_64                            2/4
  Cleanup    : python-tevent-0.9.31-2.el7_4.x86_64                          3/4
  Cleanup    : libtevent-0.9.31-2.el7_4.x86_64                              4/4
  Verifying  : python-tevent-0.9.28-1.el7.x86_64                            1/4
  Verifying  : libtevent-0.9.28-1.el7.x86_64                                2/4
  Verifying  : libtevent-0.9.31-2.el7_4.x86_64                              3/4
  Verifying  : python-tevent-0.9.31-2.el7_4.x86_64                          4/4
Removed:
  libtevent.x86_64 0:0.9.31-2.el7_4    python-tevent.x86_64 0:0.9.31-2.el7_4
Installed:
  libtevent.x86_64 0:0.9.28-1.el7      python-tevent.x86_64 0:0.9.28-1.el7
Complete![root@smeserver-10 ~]# rpm -q libtevent
libtevent-0.9.28-1.el7.x86_64
[root@smeserver-10 ~]# samba --version
Version 4.4.4
[root@smeserver-10 ~]#