Make wallpaper_file a mlstrustedobject to permit writes from any app level.
diff --git a/system.te b/system.te
index 6389b0e..7232af7 100644
--- a/system.te
+++ b/system.te
@@ -148,7 +148,7 @@
 # Relabel wallpaper.
 allow system system_data_file:file relabelfrom;
 allow system wallpaper_file:file relabelto;
-allow system wallpaper_file:file r_file_perms;
+allow system wallpaper_file:file rw_file_perms;
 
 # Property Service write
 allow system system_prop:property_service set;