[ros-users] How to overlay a package in ros core?

Hello,

If I wanted to install a modified version of a package in ROS core (e.g.
message_filters) without removing the old version, how would I do it?

I have ROS C-turtle installed via .deb packages in /opt/ros/cturtle/...,
I have a local package directory in $HOME/ros/packages, and my local
installation directory is listed first in my $ROS_PACKAGE_PATH. For
non-core packages, this works OK. But rospack always looks in $ROS_ROOT
first, regardless of what's in $ROS_PACKAGE_PATH (see line 1606 of
rospack.cpp, SVN revision 10588), so it will ignore any overlay for
packages in $ROS_ROOT. Is there another way to overlay core packages?

Thanks!

Mike