Stephen munt

Hi, new and learning to become a fire risk assessor . Im studying about fire doors and im just wondering. it a fire door has a "fire door keep shut" would you still be able to fix a the automatic door closers like the "Dorgard Fire Door Retainers" ? would you have to replace the sign with a new sign "fire door" or would it be acceptable to ? And also going off the subject a little, would the manufacture of the fire door be able to clarify if you can screw door closer devices like the above or would it make the fire door invalid ? Thank you Stephen

Thank you very much for your advice. And I'll pass this advice to the shop owner. Ps I I do know the class types and have no idea why I put the electrical in class A lol. Thanks again Stephen