I have just started learning PCB Design (using Altium Designner) and I have a basic question about PCB Rule set. Rule set is defined by the Altium, but can we edit the rule set according to our priorities?
Absolutely. In fact, one of the first things you should do is to set up your templates and customize the design rules to fit your needs. Talk to your PCB manufacturer to find out their preferences and adjust the rules as required.
As you design PCBs, you'll find that some rules need to be tweaked and you can do that on a per-design basis. If you see that you do the same changes over and over again, then just make those changes on your templates and they will be there for your next project.
Same thing applies to schematic, project, output job and other templates.