All building codes require that manufacturer's installed equipment be installed in accordance with the manufacturer's design and installation instructions.
Installing an 8' attic ladder in a 9.5' ceiling is not in keeping with the manufacturer's installation instructions nor is altering the original equipment to make an extension.
Doing both is not only safe, it is illegal and poses a hazard to both you and any future owners.
You can find the codes at your local code department of your municipality.
The proper solution would be to replace the attic stair with one properly sized for the ceiling height.
Short of that, you're creating potential hazards for yourself and anyone else who tries to access the attic via this defective equipment..