The maximum number of letters of recommendation is one of the very few things schools don't really care if applicants follow (based on what I have heard and my own experiences).
There is good reason for this, though. If you use a committee letter from your university, you don't really have control over how many letters are included. Mine had like five I think, and I couldn't ask my university to take any out and upload a new AMCAS file just for schools that requested four letters at maximum.