Character styles can be as simple as a font style or a color. To create a character style that just adds bold styling (we’ll call it BOLD), set up the style so that the only characteristic chosen is Bold from the Font Style menu in the Basic Character Formats pane of the Character Style Options panel (whew). You could then style text with a paragraph style that uses Times, for instance, and apply the BOLD character style to the characters you wish to become bold. If the paragraph style font changes to Trebuchet, the styled text would update to Trebuchet Bold. Trust me, the setup is quicker than the explanation of it and you get the added feature of not having local overrides which get left behind when styles change.