How to modify the existing thingworx Extension and build in JAVA

Articles:

• "How to customize a Widget and an Extension in ThingWorx?": https://www.ptc.com/en/support/article/CS238765
• "Ability to modify User Extensions programatically in ThingWorx": https://www.ptc.com/en/support/article/CS189906
• "Improved in-place upgrade of extensions with Java-backed entities in ThingWorx 8.3": https://www.ptc.com/en/support/article/CS287539
• "Is it possible to edit ThingWorx extension without original source code files": https://www.ptc.com/en/support/article/CS375938
• "How to import and upgrade ThingWorx Extensions": https://www.ptc.com/en/support/article/CS233011