updating a style without losing customisations

[AliceHoward]

You need to download the xml of your customised version to your PC, then download a copy or WINMERGE, using winmerge you can do a side-by-side comparison of your customised xml with the new updated xml.

The methods you have been trying will not have worked and can never work, think of the child style in the way of actual children, you cannot have a child before a parent, the parent is always the style already on your system (database) the child is always added to the existing parent style (on your database)