@boganoba Tray files don't themselves contain any data from mods or custom content. If a lot uses cc, you'd need to have that cc installed in order for the items to show up, but the data from cc files isn't part of the lot's data. So no, you don't need to remove the contents of Tray before patching.
It is however a good idea to backup either your entire Sims 4 user folder (the one in Documents > Electronic Arts) or the subfolders within it that have data you want to preserve (e.g. the saves and Tray folders) before patching, or at least before launching the game after installing the update. That way, if something goes horribly wrong, you can just restore the old files or add them to a clean Sims 4 folder with nothing lost.
