I'm not sure what this means. Logic's articulations are only a sequence of data sends, often keystrokes, though sometimes CC data. Logic is unaware of what actual sounds are generated in its Articulation Sets.
Fear not. As you say that you can select all of your target notes in Piano Roll (viewing multiple tracks at once), you can use key commands. Go into the KC menu and search "Articulation." You'll find KC's for articulations 1 to 32. Though I have not proofed this, any selectable note in Piano Roll (no matter its home track) should respond to Set Articulation commands.
So "Set Articulation 1" "a" would set everything to that vowel, "Set Articulation 2" "e" likewise.
You'll need to assign those KC's. They have no default.
As for doing this by bar, that would require setting the cycle to the bar, then "Select Inside Locators," then perform the KC.