I develop on renesas-ra platform and it uses platformio/framework-arduinorenesas-portenta@1.0.4 package. The package is based on GitHub - arduino/ArduinoCore-renesas repository. The latest release in the repo is 1.0.5 however.
How can I create my own package platformio/framework-arduinorenesas-portenta@1.0.5 out of it and use it in the project?
Extract it somewhere (7zip). Then copy over the old C:\Users\<user>\.platformio\packages\framework-arduinorenesas-portenta\package.json to where you extracted it, at the same directory level as the platform.txt. Change the version field in that copied package.json accordingly to indicate 1.0.5.
You should then be able to point PlatofrmIO to this package with platform_packages in the platformio.ini of the project: