I think you have 3 potential choices:
- Change your Android reading app to one that is better suited to automatically honouring the epub internal CSS styling, e.g. Bookari, PocketBook, UBReader, Aldiko to name but four. I'm sure there are many more.
- If they exist, change the settings in your current Android reading app to obey existing internal CSS rather than overriding it with your device preferences. I think FBReader, CoolReader, Moon+ let you do this. Depending how well/badly formatted your original epubs are, this option may create more problems than it fixes.
- Stay with your existing Android app which I'm assuming lets you ignore all epub internal styles and replaces them with your device preferences. But find a way to change all HTML markup containing '***' to one of the lesser-used heading tags,
e.g. <h6>***</h6>
You can then use your app's CSS overrides to centre all <h6> headings.
To change the HTML markup you could use an epub editor (calibre or Sigil) on each individual book - time consuming. Or maybe you could look at calibre's Search/Replace option in its conversion settings to see if you could get what you need via a bulk epub-to-epub conversion.