Identify the current door
Keep the model, size and available product approval reference. A proposed glazed section needs to work with the specific assembly. A window layout from another product family may look suitable while requiring different construction.
Compare supported paths
Ask whether the manufacturer offers an appropriate glazed section or whether a complete new door is the practical option. Discuss the effect on door weight, hardware and the counterbalance as part of the professional assessment.
Review the revised configuration
Confirm the applicable product and project documentation before authorizing a change. Also consider sight lines, interior lighting and the desired level of privacy. The technical decision and the appearance decision should both be settled before work begins.
Your questions
Can a contractor simply cut windows into a solid panel?
Do not assume field cutting is supported. Ask for the manufacturer-approved approach and the documentation for the resulting assembly.
Will using small windows keep the existing rating unchanged?
Window size alone does not establish that. The particular glazed configuration needs to be reviewed against the product documents.