You can apply the chord highlighting, text size, chord size, chord diagram information, and overall style preferences of a certain song to other songs in your library as long as you are using plain-text files for your songs (as opposed to PDF, JPG, PNG, SongSelect, Microsoft Word, or other similar types of file types).
You can do this by first navigating to a song that has your desired style > tap the Style Preferences Menu (the sliders icon in the overhead menubar, next to the gear icon) > tap the three dots in the upper right of this menu > tap All Songs, Current Book, or Current Set depending on which one you would like to apply your current song's style to. If you desire, you can also tap Future Songs in this menu to apply that style to all future songs that you import into your library.
Again, keep in mind, this will automatically apply all aspects of the Style Preferences Menu of your current song to whichever option you choose, including text size, chord size, font type, chord highlighting, etc.