I have a list of items that I want to change from Arial Regular to Arial Bold and then back. My voiceover will read the list, and I want the words to go BOLD to correspond with the VO.
If I placed markers on the text layer to create IN and OUT points, could I use an expression to control the font this way?
Fonts cannot be controlled with expressions and that is that. You have to use differently formatted layers, cut and edit them suitably. What you want would look iffy, anyway, since the transitions wouldn't be smooth due to different kerning etc.. Same old limition of non-monospaced fonts. If you're still interested in doing this semi-automatically consider otehr options like adding a stroke text animator or one for color and animating those, which could be based on markers or otehr automatisms using expressions.