If you're setting the text inside Animation Composer panel it overrides the text layers inside the precomps. You can still change the text inside the precomp, but only if you haven't changed the text inside Animation Composer panel before.
Setting the text inside Animation Composer panel allows you to have different texts on each layer (you can just duplicate a layer and change text easily), but you loose the ability to make parts of the text bold. This is something we would love to add in future versions.
Video: Changing text inside a precomp
Video: Changing colours on a specific word
To change the colour of a word you may need to do one more extra step - disable a "Fill" effect that is present on each text layer. Here is a video showing how to do that: