Fire door modification beyond trim allowance

So I bought some fire doors.

"The doors comprise cellulosic (flaxboard) cored, timber framed leaves". The Certifire certificate of approval is here: https://www.jeld-wen.co.uk/getmedia/0b0aa417-28ea-42ba-9513-489469a53773/CF160-Certifire-certificate-FD30-Timber-Door-Assemblies-44mm-FD30-Moulded-Doors.pdf.aspx

These are standard sized doors that have a maximum trim allowance of 4mm on each side and 6mm on the bottom.

The problem I have is that my house was built in the late 1800s and there is not a standard sized door opening in the house. There’s not a huge amount in it, but if I were to trim the doors, doing so would exceed the trim allowance and presumably invalidate the Certifire certificate.

My thinking when buying the doors was that I would take off the door linings then adjust the openings before fitting new door linings, stops etc.

However, we’ve had carpenters round to quote us for fitting the doors and to find out if there are less disruptive ways of going about this. The three people that have come around have all quoted us for fitting the doors to the existing openings. One has suggested modifying the doors by sawing off one or more of the timber frame edges, removing some core material before putting back the timber. They believe this would get the job past Building Control, especially since the door will be painted afterward.

However, as I see it, this would mean invalidating the Certifire certificate as far as I can tell, whether Building Control signed it off or not.

So let’s say I put my concerns aside and got someone to modify and fit the doors in that way.

• Q1. How likely is it that this would be signed off by Building Control?
• Q2. If it was signed off, in the event of a fire, would we be covered by our insurance?
• Q3. If we rented the house, in the event of a fire, would we be liable?
• Q4. If we sold the house, in the event of a fire, would we be liable?