Is it possible to create a new component in the library from an existing one “on the go”. For example, if one goes to Eeschema and clicks “Place Symbol” to choose a symbol, then if the symbol doesn’t exist, they can create one (from some dialog box where they input parameters) and the symbol is placed in the library automatically?
KiCAD does not have the capability you describe, in a general sense. You can, however, place an existing symbol and then alter its value, as well as its associated footprint.
As an example, you might place, say, a resistor symbol. You can change its value - e.g., 30.1 ohms rather than 10K. You can change its footprint - a 2-watt, through-hole part instead of 0805 SMT. You may re-assign its reference designator from R17 to PS1. But you can not (within EESchema) change its appearance to look like a coupled inductor.
If that’s what you want to do, you need to open the symbol in the Symbol Editor. This is actually easy to do - hover the cursor over the symbol and press “Ctrl-E”. Or, if you’re like me with a superannuated mind that can’t remember whether the green side goes “up” or “down” when I’m laying sod, hover the cursor over the symbol, do right-click, select “Edit Component” -> “Edit with Library Editor”.
Thank you, but would it be possible to alter the source code (on my own) to do this capability?
KiCad is Open Source, so it’s possible to make modifications. Check out the Development section of the website.