You can't apply an effect to a single region within a track. You have to apply it to the entire track.
However, you can automate the effect so that its parameter can change throughout the timeline. For example, you can have a 'verb whose mix is very wet during one part of the song, and dry during others. You can be very specific, drawing many, many nodes and changing any (or almost any) parameter of the effect, just as you would with a volume or pan curve. You can even toggle the effect on or off at any time, with automation.
That being said, if you're not running into a performance limit re: cpu and disk speed, it might actually be easiest to split parts onto new tracks and load the effects you want for each part. If I had a clean guitar with chorus during the verse and a dry, distorted guitar with octave doubling for the chorus, I'd probably put them on different tracks. Otherwise I'd have a hard time keeping my head straight when mixing.
Also, something I didn't know is that a lot of folks with use the verbs on an aux channel, rather than separately on each track. Then each track can dial its aux send percentage to the verb without having multiple instances of what can be a heavy cpu-load effect.
Let me know if I can clarify the concepts or get you started with the specific keystrokes for doing the above. FWIW, I really learned a lot from this book:
linky