First question: No. The outlier threshold applies equally to all levels (concentrations) of qualifiers - it's not possible to give lower level concentrations larger error windows. This is something that has been requested in the past - and has been logged in our enhancement system for consideration in a future release.
Second: There is no way for a user to override an outlier flag - however, we can register that an analyst has approved it (and which will appear on the report). However - this approval is at the sample level (meaning approved for all compounds in one sample). Once approved - this flag can be added to be displayed in a report: