Add new gene/var to scanpy object

Hi there,
Thanks for the tools. Much appreciated.
I have analysed my single cell data using scanpy (clustering, annotation etc.)
But, then I have added GFP to my reference and run cellranger again on the same data from scratch.
My question: is there any way to added GFP gene alone from the new data to the previous analysed data? if yes, what is the best way to do that.