Use the tool TileIconifier to create a custom link with a different icon.
Run the tool, click on "New custom shortcut", select here the tab "Windows Store", here select the app and create the shortcut.
In the main menu, select the shortcut of the app, double click on the
medium icon entry and select the custom icon from an exe or your own .ico file and press
In last step, click on Tile Iconify
Now on start->all app->TileIconify, you see the new shortcut with the new icon, do a right click on the icon and select
pin to start.
Now you have the modified icon on start.