currently user have $JVM_OPTS - they are used before automagically generated ops.
+1, although as a nitpick I'd prefer the variable be named JVM_EXTRA_OPTS instead of JVM_OVERRIDE_OPTS, since its value won't actually override the other JVM_OPTS.
Adjusted patch according to my last comment.
Integrated in Cassandra #1251 (See https://builds.apache.org/job/Cassandra/1251/)
add support for JVM_EXTRA_OPTS env variable to cassandra-env.sh
patch by Radim Kolar; reviewed by Paul Cannon for CASSANDRA-3476
jbellis : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1212843