[AstroPy] Inverting SkyCoord spherical offset transformations

[Warren Hack]

Hello,

The astropy documentation provides a very useful example of how to 
compute the offset between 2 SkyCoord positions at 
http://docs.astropy.org/en/stable/coordinates/matchsep.html?highlight=spherical_offsets#separations. 

Specifically, the example for "spherical_offsets_to" in that section of 
documentation shows how to derive a delta RA and delta Dec for those 
source positions.  In my case, though, I already have the delta RA and 
delta Dec from an astrometric solution for that observation and want to 
apply those deltas to the source positions to reproduce the astrometric 
catalog positions.  So, the operation I am really interested in would be 
the inverse of this example where those deltas would be applied to the 
"bright_star" SkyCoord position to reproduce (within machine precision) 
the "faint_galaxy" position in RA and Dec.

It could be that some other functionality in Astropy would be more 
suited to providing the right answer to this problem, but the 
documentation does not provide any indication of how to do this (at 
least not where I could find it).  Any pointers would be appreciated.

Thanks,
Warren Hack