I re-use rigs all the time. If it was catching fish at the end of one session it will catch fish at the start of the next.
I don't though, purely for aesthetic reasons, extend rigs with extra line. Because I carry so few variations I have plenty of new spares if I need longer rigs on a new venue. But I take this one stage further being a skinflint, or abhorring waste, depends on your point of view. Shortened rigs get used on my club lake and stored in a dedicated box. Rigs that become too short get re-made as margin or up in the water rigs. Finally from those rigs that are too short or I don't need to make more margin rigs I save the line and use it for hooklengths.