Is there a way use an RDP to configure a continuous offset from GPS calculations?
Those offsets are normally used in differential gps. A fix point (station) knows it exact location (from manual measurments), calculates from the gps data the requred offset for correction and send this (quasi constant) offset (ex. 2.5m SW) to you.
The  assumption is that if you are close to this station the atomospheric error (=offset) is valid also for your position in some distance.

Im not too familiar with android, but you could send manipulated D-GPS data maybe?

For radio those are send with RTCM (Radio Technical Commission for Maritime Services), (you can get down to 2cm accuracy) - for mobile phones you need to stitch to Ntrip (Networked Transport of RTCM via Internet Protocol): http://www.rtcm-ntrip.org/home most of them are non free/paid, so you need to look around (if you really want there a ways to make your own low cost server (raspberry pi..))

would you still need offset if the accuracy is already very good? Boosting accuracy seems easier!

Have a look at https://play.google.com/store/apps/details?id=com.lefebure.ntripclient
==> ACCESS_MOCK_LOCATION - Used for routing external position data to other applications. but this solution has also it downsides :-(