I cannot verify the validity of the older answer since I cannot find a way to set any attribute to something like “undefined” or “inherited from…”.
The only way I can suggest is therefore to create the respective style anew from scratch without touching any attribute you do not want to set, the new style formally inheriting from ‘Default’ only which seems to be a style of a “very special behaviour”.
I would support a feature request concerning an pseudovalue for attributes. The needed base of the functionality should already be implemented. (See CF e.g.)
There also is a specific case where something like an “undefined” option is available: the ‘Language’ setting under ‘Format Cells…’ > ‘Numbers’ offers a variant "Default - " followed by the preset locale.