Can I add to a vector library?

Hello - Yes you can make library by inkscape or Krita itself granted they are vector and formatted as symbol/ or many symbol.

I have done so several times; Though I’m more familiar with the notepad method since I do more than 10 symbols in one library.

Me and @AhabGreybeard have different written method you can use. There is a guide as answer to a previous question. A starter file can be found on this thread.

Goodluck.