Re-storing decanted oil, and varnish lifespan.

[AESamuel]

Just a couple of really quick questions!

If I decant danish oil into a separate container for use, can I pour the excess back into the original bottle without any problems?
&
How long will a home-made wiping varnish (50/50 white spirit/poly or varnish) last in an airtight sealed jar?

Thanks a lot!
Asa