I believe 3.6.1 addresses combination of WPS's. A combination of them can be done provided the limitation of essential variables applicable to each "process" is observed.
Process as defined by AWS 3.0
process. A grouping of basic operational elements used
in brazing, soldering, thermal cutting, thermal spraying
or welding.
and a couple of more references from AWS 3.0
submerged arc welding (SAW). An arc welding "process"
flux cored arc welding (FCAW). An arc welding "process"
shielded metal arc welding (SMAW). An arc welding "process"
I only quoted the first four words of the process, but they are the relevant words.
Based on that, yes it means combination of processes and WPS's as long as the essential variables
of each process are observed.
I know for sure that ASME allows, I believe this portion of D1.1 allows it.
Regards,
Gerald