Q: Re-use redemption codes?

I have tried to download movies on ITunes at work using my ITunes username etc, but my work's computer and internet.  However, the connection is crappy (Window computer).  Can I re-use the redeption codes to download the movies when I get back home, using my IMac and internet?  If not, this is a really bad idea cuz I would assume many people have connection problems, particularly with Windows computers.

I would appreciate any help and advice whatsoever.

Thank you.