I create songs with drum patterns and bass lines to play a live solo piano act with. I have a song that i have copied. It is using the same drum pattern, I will record a new bass line, but i want it to be 16 measures longer than the one i have copied. Basically I want to add 16 measures of the drum pattern without having to do everything over. Is there a quick simple way to do this

In order to decypher what you are doing - can we agree that when you are talking about the Motif XS you use the word “Song mode” and “Pattern mode”.

It matters which mode you are in as to how measures can be added and/or copied. SONG mode is linear and plays from start toward finish - which is always a set number of measures. PATTERN mode is made from looping musical Sections that play over and over endlessly.