Is it less painfull to extract a tooth after doing root canal ? (root canal many years ago)

A RCT extraction: RCT removes the nerve from within the tooth & in doing so prevents the transmission of sensation from the tooth when exposed to heat, cold & sweets. The outside of the tooth still has live tissue that connects it to the bone. Therefore a RCT tooth will not have more or less sensation to being extracted. HOWEVER, in all cases you will be completely numb and not feel anything & so it's a moot point.

Nope: With adequate anesthesia, you will feel nothing either way.