Yes, a filler plate can be used to cover an EPT prep as long as it is made from the same material as the frame.
This information can also be found in NFPA 80 under Chapter 5 for Field Modifications.
Von Duprin surface mounted 6300 electric strike paper template and installation instruction are provided with the electric strike. See attached
https://us.allegion.co...
This information can be found at the following URL's:
AD200/AD250/AD300/AD400 Cylindrical http://w3.securitytechnologies.com/irstdocs/installinstructions/102104 P516-092.pdf