The changed preference won't be yours.
If we lump together even a fraction of my life as "me" rather than just me-this-instant, we'd find that my preference is actually pretty malleable while preserving the sense of identity. I think it's within the realm of possibility that my brain could be changed (by a superintelligence) to model a different preference (say, one giving much higher weight to versions of me that win each day's lottery) without any changes more sudden or salient to me than the changes I've already gone through.
If I expected this to be done to me, though, I wouldn't anticipate finding my new preference to be well-calibrated; I'd rather expect to find myself severely surprised/disappointed by the lottery draw each time.
Am I making sense in your framework, or misunderstanding it?
This is our monthly thread for collecting arbitrarily contrived scenarios in which somebody gets tortured for 3^^^^^3 years, or an infinite number of people experience an infinite amount of sorrow, or a baby gets eaten by a shark, etc. and which might be handy to link to in one of our discussions. As everyone knows, this is the most rational and non-obnoxious way to think about incentives and disincentives.