Update Basemap Layers
Consider using vector layers for performance, link from Robert:
From an email
There are a few basemaps available through ArcGIS online that align with these new boundaries more closely than our old basemaps. I've found an updated grayscale, an updated street map, an updated terrain layer, and our satellite basemap does not have any borders (so we avoid any awkwardness there). While none of these options are perfect (except maybe the terrain/national geographic map), they all at least update the Western Sahara region.
Grayscale (https://www.arcgis.com/home/item.html?id=979c6cc89af9449cbeb5342a439c6a76): Has Western Sahara Pretty much the same in Pakistan/India/China border when you zoom in far enough
Terrain (https://www.arcgis.com/home/item.html?id=b9b1b422198944fbbd5250b3241691b6) Has Western Sahara Has Pakistan/India/China border updated
Street (https://www.arcgis.com/home/item.html?id=bc19c34549de4000bcd91cef929420dc) More google-like than our old street map Has Western Sahara Pretty much the same in Pakistan/India/China border when you zoom in far enough