Changing ProdID on signal


I have a layout with multiple pallets and shuttle conveyors and a pallet feeder and I need to transfer empty pallets on Works Processes without pallet. My first thought was that when some of the Works Processes around robots will not have a pallet, it will send signal to the purple Works process before the shuttle conveyor and it will mark a waiting pallet with ProdID specific to that Works Process that send the signal and it will transport out the pallet. the thing is I didnt manage to change prodID on signal. I tried to make a new task in works process for it, but I failed. Any advices are welcome. I am also open to any other solution, that will lead to similiar results. Thanks in advance!