This problem was reported by itk.
It is possible to user the alter_semantics hook to e.g. change the default values of fields or change the labels.
However, these changes only take effect if the language is set to English. If the language is set to a different language, then the editor always uses the default values from the semantics file and the labels from the translation file.
In the images, you can see H5P Columns with changes semantics. If set to English, the default value for the separator is set to disabled by default via the alter_semantics hook. If set to French, the script has no effect.
alter_semantics also takes effect on default values or other fields if the language is not set to English