I would like to check if it would be possible to add the finlets retrofit for Boeing 737NG as an additional fuel efficiency upgrade on the airframe. Should give a 1.4% reduced fuel consumption in addition to any winglets installed and should have been certified by EASA since last year: https://www.airwaysmag.com/new-post/easa-boeing-737-drag-reduction-finlets
https://vcteco.com/finlets
In current model we can only support one upgrade per aircraft. So this would need to be perhaps modelled something like winglets + these.