The following article explains how to convert an AP into Unleashed(Standalone mode)
The following link is the firmware required to flash the Access point to standalone mode
Here is the User Guide how to configure Unleashed(standalone mode).
Yes. R510 if running AP1xx series firmware eg. 114, 110, 108 it can work as standalone with individual CLI and HTTP/S GUI access methods. However, it is intended to be used as intermediate firmware for discovering ZoneDirector or SmartZone controller, or Cloud.
I would suggest you look at the AP firmware 200.x series. This firmware can run an AP as a standalone or cluster of APs. Also provides more features for a standalone AP such as AVC, mobile app, URL filtering, Alexa skills etc.,