I think that the winglets use something like an xml code in the model (.MDL) that reads the line ui_wglts=0 or 1. If it sees 1, the winglets are visible and if it sees 0, they are hidden.

I have a few add-on aircraft by other developers that use a line in the aircraft.cfg to determine if something is seen or not.

Here is an example:

// Repainters note:
// Embedded in the aircraft models is code that reads the fltsim.x title and applies visual
// changes to the model based on what text is in the title.

[fltsim.0]
title=Tecnam Sierra Paint3 bluegrey Covers Fairing Nnumber

If I remove any of those three words, or all of them, they are no longer visible on the model. The idea is the same for the winglets on the CS 757.

Mark