Originally Posted by
JAXBA
1) Yes
2) a) Yes
___b) Yes 
SEA/LAS are in the same zone, so changes would only be subject to availability of course.
If you're interested, it'll be cheaper to have the LHR stopover on the way to ZRH, rather than back to the USA, as the GB tax is based on distance to destination.
Thanks !! Is there something on the web which shows which cities are in each zone?