FWIW, here's what I use to set context:
Code:
set newContext to my getContext("home")
set context of thisItem to newContext
on getContext(contextName)
tell application "OmniFocus"
tell front document
set contextID to id of item 1 of (complete contextName as context)
return first context whose id is contextID
end tell
end tell
end getContext
getContext returns the best match for a given string, so "home" would match "Home" before the "Home > Garden" context.