For things like expanded balance and transaction $ amounts, Query will automatically adapt to larger amounts, and you generally won’t need to do anything.  (The only exception is if you send the output to a vendor, they’ll need to be made aware of the larger amounts.  Or perhaps if your report is completely full side to side and you need to remove a column in order for everything to still fit across a printed page.)
As far as dates, if a date was formerly 3 separate fields for year, month, and day, and is now a single field for the full date, Query will simply delete all of the old field names from your Query entirely.  It cannot replace it with the new field, as that will have a completely different field name now.  (That’s one of the reasons to print a definition before your conversion, so you can look at the report to see what dates might be missing.) 
If a date field still has the same name but was simply reformatted to the ISO format, you may need to tweak a custom field setting (such as if you used the “SUBSTR” field to pull out the month or year from a date), or change your selection criteria.  The related FAQ below has some tips for how to construct these settings.