The inspection rules cannot be deleted. They can only be made inactive.
The original reasoning was that if you were doing some forensic investigation and a rule was no longer on the system then the database would be corrupt.
You are not the first person to ask for this and I believe Cisco is considering this feature request.
In the meantime, when you need to make a change to a rule just clone the original and then make the original inactive. In this way if you make a mistake you can make this rule inactive. You can then clone the original rule again and fine tune what you are trying to accomplish.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...