Modification
Yes you can use other versions along with the Jabs, so for this you will logically have to have the version in hand and the version has to be 1.8 from Minecraft, you can't use 1.8.1+ versions.
You will need the JabsClient installer or Jabs Launcher.
In the installer you will have to run it and choose the version of minecraft you want to join with Jabs, remembering that it has to be 1.8 or according to the version that is in the installer and click install.
Exemple:
Coming soon
To install mods is the method you know, both forge and liteloader, open the folder of your minecraft, mods and the version of your game. Remember that forge or liteloader has to be active in Jabs settings.
To enable or disable see the configuration page by clicking here.