Where are the chip configurations stored in IDE 1.6.x? How to modify them?

Question

With the new 1.6.x version of the Arduino IDE, obscurity of adding new chips has gained new level. It now seems you have to add HTTP links to some JSON files in single-line edit field in settings.

I did so and to add AtTiny to Arduino IDE, I used this JSON file: https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

I have AtTiny 13 however. It's same as the others, according to datasheet, but has different signature:

avrdude: Expected signature for ATtiny45 is 1E 92 06
         Double check chip, or use -F to override this check.
Wrong microcontroller found.  Did you select the right board from the Tools > Board menu?

I tried to search ATTiny45 and the signature over the files - no success.

What I need is to add the ATTiny13 to the list so that I can finally actually do some programming, instead of being completely helpless.

Answer 1

You are importing a json file provided by someone for free.
The best thing you can do is contribute by adding ATTiny13 to this repository.
To do so:
So go to github (create a account if you do not have one);
create a fork of the repository.
Add your ATTiny13 board to the boards.txt file.
mod the json file to contain a new version and the attiny13.
Test and if everything works fine
Create a pull request

Answer 2

This doesn't answer the original question (which was how and where to modify the board configurations) but at least solves the immediate problem.

This repository contains working and maintained profiles for Attiny13: https://github.com/MCUdude/MicroCore