I'm a bit confused with the user group settings in Mikrotik. I'd like to setup a user with read access and the ability to enable or disable configurations, but not modify them or delete them. Is this possible?

enabling/disabling is the same as modifying. So no you can't set such user. Read-only users will only be able to read config.

The only way you could do this, is to use the RouterOS API to create a custom windows (or any other OS) program, to do only things you need. In this case, list configuration, and allow to disable or enable certain rules. You would need an expert programmer for this. http://wiki.mikrotik.com/wiki/Manual:API