On the other hand, without further context "I have the right to feel like a good person no matter what I do" is a dangerous thing to internalize.

Not really. Our experiences indicate that the brain's ACL system matches rules by specificity. A blanket rule change like this one will only remove the specific generalizations matched during the retrieval process, not any broader or narrower rules. (This is implied by memory reconsolidation theory, btw.)

In fact I suspect that rules, like "If I want to murder someone, I should feel like a bad person" exist in the brain using the same mechanism. Obviously this is one rule you shouldn't get rid of.

Actually, funny you should mention, because that's an ill-specified rule right there, and it's precisely the sort I would say you ought to get rid of!

Why? Because you said "if I want to murder someone". Merely wanting something bad doesn't make you a bad person. Who hasn't wanted to murder somebody, at some point in their life?

If the rule you state ("If I want to murder someone, I should feel like a bad person") were a genuine SASS rule that you'd internalized, then every time you got mad enough at somebody, you'd suppress the anger... and keep right on feeling it. Most likely, you'd have people or situations you'd avoid because you'd feel chronically stressed around them -- vaguely angry and disappointed in yourself at the same time.

Usually, though, unless you actually said you wanted to murder somebody when you were a kid, and shocked an adult into shaming you for being bad, you probably don't have an explicit SASS rule against wanting to murder people, and don't actually need one in order to avoid actually murdering people. ;-)

Negative SASS rules are compulsions that override reflective thinking and outcome anticipation; they hijack logical thought processes and direct them into motivated reasoning. Oddly enough, positive SASS rules don't seem to have the same degree of power... although it occurs to me that perhaps my current model is flawed in this description of "positive" and "negative" -- better words might be "surplus" and "deficit".

(That is, if your brain thinks a desired positive SASS quality is scarce, you can be just as compulsive in acquiring it, as you can be compulsive in avoiding things with negative SASS. However, the rules themselves seem to influence what levels are perceived as surplus or deficit, so there's a bit of recursion involved.)