wilderness - 8:58 pm on Dec 6, 2012 (gmt 0)

You need mod-rewrite to capture strings.

SetEnvIfNoCase User-Agent "chrome" myNewVariable=A

this line ends reading after the exactly as ("chrome") denying all browsers where the UA contains chrome and never reads the variable string.

Apache does solve some issues on its own, whether the result is what you desire, and/or to your liking, ia another story.
Surprising the line doesn't generate a 500 Error.