Override wallpaper with VMware AirWatch Agent
In general, the success rate of overriding MDM enforced configuration changes is very low. Pragmatically:


You can remove the management profile and then make changes as you see fit. 
You can request your device be moved to a different group under air watch that relaxes that restriction. 


There could be a bug you could exploit, but Apple and/or air watch would likely patch that since it would also likely be a noticeable failure.