You can create a Adobe Acrobat preflight with a fixup to remove all printer marks.
Then you must use it as part of a Freeflow core Preflight node in your workflow before imposing.
Please find attached the Acrobat preflight file.
Hope this help you.
There are two possible ways to do this.
The simple way
The optimize component has a Remove Printer's Marks component. I would use that first (this assumes that marks were created by a graphic communications program).
The less simple way
Use the preflight component to select and delete objects based on their properties. FFCore preflight uses the pdfToolbox engine. FFCore can execute preflight profiles from pdfToolbox or from Adobe DC Professional.
For this case you need to first define a preflight check that will match against the objects you want to delete. If the PDF has a properly defined trimbox then it could be as simple as checking for objects completely outside of the trimbox
This will require some trial and error but I expect that you would ultimately be able to define a check that will catch the objects of interest.
Once you have that check then you would want to build a preflight profile with a fixup to remove objects. This fixup can be constrained to objects that match a specific preflight check (e.g. the check for objects outside of the pdf trimbox.