Have a question namely I play Minecraft with mods on version 1.7.10 if I add now to a new version (1.12) mods there are problems there, I use the McModinstaller
Because you do not need the ModInstaller anymore.
Just put in the mods folder.
Forge and other stuff will be installed over the jar
You can't use a 1.12.2er mod in 1.7.10. They do not work there.