Is it possible to assign net name to the symbol term in the schematic through skill without creating wire(wire stub) from the terminal?
Yes, you can do this with dbCreateInstTerm. However, if this is a normal schematic, the information will get lost if you open the schematic and do a check-and-save (or call schCheck from SKILL). So if you want it to be a human-editable schematic, you need to follow the schematic editor's semantics.
I have another question.The reason I wanted to assign nets to the symbol terminals was to create wire stubs with my net names.
But it looks like that schHiCreateWireStubs() removes net names from the terminals and creates stubs with terminal names(D,S,G,B) rather than my assigned net names.
Do you know how can I do this?
schHiCreateWireStubs() won't expect the instTerms to be there already - if they were in a normal schematic it would be because the wiring is already present - and so no need to create a wire stub.
So if you want to add wire stubs, you'll have to use schCreateWire() to do it yourself.
As I said, the key thing is that you have to follow the schematic editor's semantics if you're going to use the schematic editor to edit the design.