I am very tempted to get into the guesswork game on why it eventually worked for you. I have a theory but it really is neither here nor there since what matters is getting it working. One part of my guesswork suggests that you may have shown the avast team that they have some re-working to do to make the exceptions effective.
Part of that guesswork is, perhaps more to the point, that currently the exceptions are only relevant if a problem is first discovered. That would mean that predefining exceptions - as I attempted - is an exercise in futility and that the exceptions are only consulted when a suspected rootkit is discovered but (in a kind of chicken and egg issue) having attempted the exception by you may - at least for now - be essential to allowing the ensuing real exception to be set in the avast4.ini.
I am well convinced that, up to this point, Standard Shield and on demand exclusion lists are completely and utterly irrelevant to the rootkit scan. Further, if they had any relevance at all the avast team would have said so before now.
I suspect you may well have assisted the team to improve this aspect of avast in the future. That may never be publicly acknowledged but at least you have my respect for your testing efforts.