Yes, you can!
When the map is submitted for approval, it is submitted to different part of the system - in fact, a copy is added to the Historical map archive.
This means that after you have submitted the map for approval, you can change as much as you like without affecting the submitted map.
For the map that has been submitted for approval - and is now actually in the historical map archive - you can change downloadable snippets, but you cannot change information or outlines for the map if it has been added to the historical map archive via an approval.