1. no
2. no

Assuming a proper match, the system if properly installed will give you optimum efficiency and performance, any alterations will reduce both.

Reducing airflow within limits can (and I say this carefully) add to comfort by increasing the latent capacity of the machine but the equipment needs to be sized correctly. It will however not aid in the efficiency.

Your best bet is to follow all the mfg's instructions and attend as much factory training as you can, if you do that, your customers will be happy and you'll be rich.