Do not ever run Keyboard Maestro 7 after running Keyboard Maestro 8. You can revert to Keyboard Maestro 7, but unless you do it carefully, the reversion will lose chunks of your macros (any actions that have been converted to newer versions, like the new generalised Search & Replace and Filter actions).
So if you want to keep Keyboard Maestro 7 around, I would suggest you compress it in the Finder, and then delete the original. However there really is no point in keeping around the old version because all the old versions are available from our archive site (https://files.stairways.com/).