For Rotterdam isn't hard to do yourself.
Open the Sim.cfg of the FSDT_Baggage_Loader, search for KLM and change its coatl.icaoprefix = EH into EHAM. This will limit KLM to EHAM while with EH, KLM appears on all Dutch airports. I think that will do for the handler. If not then you'll have to do the same with the different Stairs Sim.cfg's
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For Schiphol it works about the same. I looked up Swissport in the Baggageloader Sim.cfg If they handle Schiphol then i need to add EHAM to its icaoprefix. Same with the other handlers.
Regards, Gerrit