possibly with
ncap2 -h -O -s 'crs=-9999' AWAP_GRIDS_1961.nc AWAP_GRIDS_1961_v2.nc
ncatted -h -O \
-a spatial_ref,crs,c,c,'GEOGCS[\"GCS_WGS_1984\",DATUM[\"WGS_1984\",SPHEROID[\"WGS_84\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.017453292519943295]]' \
-a grid_mapping_name,crs,c,c,'latitude_longitude' \
-a longitude_of_prime_meridian,crs,c,d,0 \
-a semi_major_axis,crs,c,d,6378137 \
-a inverse_flattening,crs,c,d,298.257223563 \
-a grid_mapping,Rain,c,c,'crs' \
-a grid_mapping,Temp_max,c,c,'crs' \
-a grid_mapping,Temp_min,c,c,'crs' \
-a grid_mapping,VapPress09,c,c,'crs' \
-a grid_mapping,VapPress15,c,c,'crs' \
AWAP_GRIDS_1961_v2.nc
possibly with ncap2 -h -O -s 'crs=-9999' AWAP_GRIDS_1961.nc AWAP_GRIDS_1961_v2.nc
ncatted -h -O \ -a spatial_ref,crs,c,c,'GEOGCS[\"GCS_WGS_1984\",DATUM[\"WGS_1984\",SPHEROID[\"WGS_84\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.017453292519943295]]' \ -a grid_mapping_name,crs,c,c,'latitude_longitude' \ -a longitude_of_prime_meridian,crs,c,d,0 \ -a semi_major_axis,crs,c,d,6378137 \ -a inverse_flattening,crs,c,d,298.257223563 \ -a grid_mapping,Rain,c,c,'crs' \ -a grid_mapping,Temp_max,c,c,'crs' \ -a grid_mapping,Temp_min,c,c,'crs' \ -a grid_mapping,VapPress09,c,c,'crs' \ -a grid_mapping,VapPress15,c,c,'crs' \ AWAP_GRIDS_1961_v2.nc