The "Apply [stylename] and..." options in the Text Styles panel include one that clears text formatted via character style. There doesn't seem to be an option that clears text formatted by hand—"hard" formatting, without use of a named character style. I've tried all of the options to see what they would do and none clears that kind of local formatting.
Does Publisher have any other command (after the fashion of MS-Word's and other programs' Control+Spacebar) that returns highlighted text to the current paragraph style's default underlying characteristics?