As your Greek epigraph is within English context, UEB Sections 4 and 14 are indeed the place to look for guidance. UEB Section 4.5 only applies to Greek letters and, as you have pointed out, the epigraph is a passage.
You have also mentioned that Greek breath marks are involved. If you turn to page 200 of the UEB Rules, you’ll see a listing of the Greek rough breathing mark. You can find the spiritus asper (rough breathing sign dots 125) and where to place it, as well as the spiritus lenis (smooth breathing sign dots 356) in the section Greek (International) in World Braille Usage, Third Edition. This publication can be found at http://www.perkins.org/international/world-braille-usage. Turn to pages 185-187 for the information you need.
As to code switch indicators, I feel you have a few choices depending on your print sample:
1. UEB 14.2.2 would allow you to not use code switching indicators. You could apply this if you determine the location of the epigraph warrants this approach. 2. You could use the code switch passage indicators that you mentioned in your question. If so, use (3)(5)(23456) to close. 3. UEB 14.3.3 gives you the option of modifying the opening UEB passage indicator by augmenting it with an identifier. You could use the Greek (International) sequence listed on page 204 of UEB Rules. This would be especially appropriate if you use the braille characters for the Greek letters and breath marks from the Greek (International) section of World Braille Usage.