To make it a little easier I use different versions of this:
1. Make a backup of saves and mods folders.
2. Create a folder to hold the modpacks (see folders I use)
3. Copy the selected mods ands saves to the respective folders in the mod-packs.
4. Place the .bat-files in the game folder.
5. delete saves and mods folders and files in game folder (you have the backup - right?)
1. To change mods Factorio must be terminated (exit)
2. Double-click the apropriate mod-pack .bat (2x enter to confirm and close)
3. start Factorio.
.bat-files are for windows
linux users will just make their own scripts
Mac users - I don't know.