The question is, how should the application behave when the user edits their day-to-day availability, then changes their general pattern? Should the changed pattern override any specific settings to individual weeks?
That is what I have found most calendar/diary applications do.
For examplyexample GMail's calendar will let you make changes to individual instances of a series (recurring pattern), but when you change the series as a whole, it warns you that individual changes will be lost.
You could of course be a bit more flexible and show the (future) exceptions with the warning and allow each of them to be kept or discarded. You may have to do some user interviews/testing or statistical analysis to figure out what the best default for keeping / discarding may be. The number of "exceptions against the pattern" may also be a trigger to select either keep all/discard all as the default.
If you really want to be kind, show the exceptions against a (more lightly coloured than normal) background of the new pattern, allow each to be kept/discarded individually and provide a keep/discard all remaining exceptions (for which no specific decision was made).
