Evan Abrams shares a technique for animating typeface weights in After Effects showing how to create a morph between regular weighted text to bold using After Effects Shape Layers.

Morph your text shapes from regular weight to bold, black, italics, whatever

With some good old-fashioned elbow grease, Evan shows how to morph between different font weights by creating shape layers from the text creating paths, and animating the path shapes over time by copying and pasting the bold text paths onto the regular weight text at a different position in the timeline.

Evan provides some tips for adjusting the transition between the paths by setting the first vertex point in each.