I have a single-page online app which relies on query strings. Google Analytics tracking was added, however canonical meta wasn't added until a few days later, so now Analytics is showing several entries for the same page because of a difference in the query string, e.g. "/app/?s=4324,543,12421" and "/app/?s=5234,86754" whereas the canonical is just "/app/".
Is there a way to merge data for the extra pages (in Reporting > Behavior > Overview) in GA which have since been canonicalised?
To my best knowledge there is no way to change historical data (except for a hackish solution for transaction data). While I can't recall a single sentence in the documentation that says "we don't reprocess historical data" it is implied at several occiasion (i.e. things like dimension widening are not applied to historical data because it won't be reprocessed).
Cutronis GA book says it directly:
Once Google Analytics has processed the data and stored it in the database, it can never be changed. This means historical data can never be altered or reprocessed. Any mistakes made during setup or configuration can permanently affect the quality of the data.
So alas the answer is no, you cannot do this. You can use filters to get the aggregated values (and store the filtered report as a shortcut) but you cannot change data that is already processed (within the interface - you can always export to Google Spreadsheets and work from there).