Comprehension question: addProperties vs changeDefaults in load_skin.js

[Isomorphic]

Use changeDefaults() if you want to replace attributes inside of properties blocks without clobbering the entire properties block.

[Blama]

Hi Isomorphic,

when should I use addProperties and when changeDefaults in load_skin.js? How do I know if a value was already set and needs to be changed?
I'm using recent 5.0p.

Thank you & Best regards
Blama