extending duration of notes and resulting notation

Thanks Mark,
Can I do what you suggest post hoc? I mostly seem to need to do this after I have the outline bars in place. So even though I know I'll need to extend certain notes I usually enter them with same duration and voice to begin with.

The voice assignment is done with the stems up/down mechanism? (Been a while since I used it - that's my excuse as usual anyway).
Thanks again
-John