The best chance pakistan had to "liberate" punjab/khalistan from indian rule and make it a vassal tributary sikh state for it was in 1984 operation blue star. Had they crossed the border to help the Sikh separatists and those dharmi yudhai who fought valiantly by themselves defending darbar sahib they then would have been supported by the Sikh masses of the punjab countryside and the full blown insurgency + pakistani army would have overun the indian troops in punjab which would have enabled pakistan to take Kashmir much easier.
They chickened out or slyly backed out like a snake and let the Sikhs get slaughtered while they watched from a distance laughing and hi5ing each other then getting ready for the Sikh rebel influx into pakistan in which they had already planned training camps for them to hit indian targets.
Pakistani ISI played their part to checkmate Indian R&AW who were caught oping and playing catch up. The Pakistani ISI was created by the British m16 in early 1950s whereas R&AW was created in late 1960s with heavy influence from USSR KGB. So pakistan had 10years ahead of the indians and helped with training and tactics by western intelligence agencies against USSR soviet backed Indian govt.
pakistan's support to Khalistani's were on the basis of being cannon fodder to keep indian army at bay and busy while the afghan jihad was going on and resources were poured over there. Once the afghanistan campaign was coming to an end and soviets looking to withdraw they switched their true attentions and passion for capturing all of kashmir by kicking off things there.