Is there are way to change the SPAM blocking with FOPE?
In comparision to other products you could set a High, Medium, or Low at a domain level and at a user level with the understanding that the higher you went the more false positives you may incure.
Unfortunately there isn't a setting to individually adjust the sensitivity of the spam filters.
If you are concerned that you are getting false positives, I'd recommend setting FOPE to Quarantine or "add x-header" and move the messages to junk mail folder.
Also see the following article which talks about the methods for submitting false-positives
Kemper - MSFT