Hello,
Unfortunately, you can't change settings on multiple effects all at once, there's no parent/child relationship, all are independent objects, at least currently (V14.5). You cannot apply a template to an already existing text effects in order to modify only settings and not the text. All this could be part of a subtitle system we might see with some future release.
You have to go through it one by one. Something like, create a template with new settings first, and for each, apply the new effect, copy the text, remove the old.