You can lean at any altitude. The absolute EGT number has no value except to determine peak, at what point it starts to fall. The hottest EGT is NOT the hottest exhaust valve temp. Think of EGT as a navigation instrument, you are at peak, before or past.
With a carb, you can try to lean slightly past peak and if not smooth, use a little carb heat to help fuel vapourisation. Please read John Deakin's articles. Once you understand you will not go back to the old way and do you engine and you bank account a favour at the same time.