For Example, the pressure of evaporator can be changed, also the pressure of condenser and many more parameters. What is that parameter which remain constant while others keep changing ?
Depends how far you want to go with the modifications.
You can change the working parameters of the pump, changing the flow rate. While you can't meaningfully reduce the volume of the coolant in liquid phase through compressing it, through changing the flow rates you may delay the condensation - make it occur farther down the radiator - and so the volume of the liquid phase will change. You can introduce physical changes by modifying the machine: add or remove coolant, replace coolant with a different substance that has different phase change diagrams and heat properties, you may change the tubing modifying pressures and volumes, change the evaporator, replace the coolant with one that only works through compression/expansion without phase change at all, or even change the entire principle of operation - toss the whole vapor-compression refrigeration aggregate and paste a Peltier cell with a fan to the back of the cool box.
The, only thing you can't change is that you input work in order to transfer heat, or it will cease to be a refrigerating machine.