Once you have your Personal Libraries, the below quote explains the easiest way to copy a Kicad symbol into a Personal Library so you are able to modify that symbol.
Not a great idea.
You will probably regret that decision by next year. The more you use Kicad, the more items you will need to create, modify or import. One library will soon become unworkable: it will look like the Kicad “Device” Library.
Instead, make many libraries. eg: caps, electros, resistors, pots, transformers, ICs, connectors, etc.
The problem is; if you decide to change your library system later, because it is now inadequate, everything you have done up to then, if you want to re-use parts, will have the wrong library paths. ERC and DRC, as well as possibly you, will go hysterical. 