Yes, you CAN modify exclusions and policies.
First, pause the scan.
Then, make your changes.
When changes are complete, restart the scan.
The changes you made will be applied to the remainder of the scan. Note, however, that the system will not go back and rescan the data completed prior to making the changes.
NOTE: Make sure you use COMMAS, and not Semi-Colons, to separate multiple items. For example, if your exclusion list is:
*/~snapshot/*; *.adm; *.aw; etc.
Make sure it is noted as:
*/~snapshot/*, *.adm, *.aw, etc.