Yes you can, whether it's a Purchase Order, Bill, Credit or a Statement.
What you need to do here, is send the document back to the Processing tab. From there, you need to make sure the system can't automatically apply this unwanted map next time, then apply the map that extracts the data you need.
Firstly, add a note to the document, noting what you'd like to see changed. This is done through the Activity section. From here you can also get the Map ID, so make a note of that. Then click More > Return to Processing.
To stop Lightyear from automatically using that map next time, you need to remove the map from that Supplier. Navigate to the Suppliers section, select supplier, then click Edit (pen).
Click the 'Mapping' Section along the top to see the list of all approved email addresses for this supplier. Just click the trash icon next to the email address/map reference you want Lightyear to forget, thus never applying it again.
Click Save once done. Lightyear has now 'forgotten' the Mapping Rule for the Bill/Credit/Purchase Order/Statement.
Finally, navigate to the the Processing Tab to Query/Find/Request a Map for Me that extracts the dataset you require.