In Fallout 3, I was able to add the default "Goodbye" and "Hello" dialogue topics to the mods dialogue quest so that the NPC's added by the mod would only say the lines added by the mod even though they used a standard voice type. The mods Goodbye's and Hello's had a higher priority than the generic ones. The NPC's would only say lines in the higher priority topic and never fall back on the lower priority generic dialogue.
I'm having trouble doing something similar in Skyrim. If I add new Goodbye's and Hello's to the "Misc" tab (correct?), they will sometimes say dialogue added by the mod and other times they will say the generic dialogue (about 50/50). I noticed that the generic dialogue has a priority of 50 and that all are marked with "Random" but none of them has "Random End". In the mod, I'm testing 2 lines (2 for Goodbye and 2 for Hello), the first in the pair is marked as Random and the second is marked as Random and Random End. Ideally, they would only say one of those two lines and ignore the generic dialogue.
The mods NPC's are added to a new Faction which is what it used on the Quest to check for valid NPC's. IE: If they are in this new faction, then they should say the following:
(Goodbye) [Priority 100]
- Until next time. [Random]
- Yeah, see you. [Random, Random End]
(Hello) [Priority 100]
- Can I help you? [Random]
- What do you need? [Random, Random End]
This is only for dialogue that is shown to the player once the NPC has been activated. Not for Hello's and Goodbye's that happen when you are near the NPC. I have those disabled in the NPC package (Unticked "Hello's to Player"). So one of the new "Hello" infos should play when dialogue with the NPC is initiated (Can I help you? or What do you need?) only. Then other "Top Level" topics will be shown (Has the war been hard on you? Etc). Then when exiting dialogue with the NPC, one of the new "Goodbye" infos should play (Until next time. or Yeah, see you.) only.
I have read that creating a new voice type for the NPC's is a sure fire way to "start fresh", but if at all possible, I would like to use the default voice types. There were a few mods for FO3 that added top level dialogue to all NPC's and because I used the default voice types, the mods dialogue was inherited by default. My Goodbye's and Hello's worked on my NPC's and the other mods dialogue showed up once a conversation with the NPC had been initiated. Things of that nature. A new voice type is my last resort.

I'm wondering if it still possible to do something like this for Skyrim?
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http://www.gamesas.com/topic/1359944-how-to-override-default-hellos-with-quest-specific-ones-only/