You can modify booleans --- but as soon as you reboot the live CD they are gone again.
One issue with /tmp (live CD) is that it is memory resident. I have even seen solaris systems
that are configured to always put /tmp in memory. This is both good and bad, the good is
that tmp always gets cleaned out on the next boot. The bad is that it becomes trivial to
cause out of memory failures.
On most multi-user systems it is much better to have /tmp be a partition that is mounted
during boot. The advantage is that it is impossible to OOM the system, second, it is
possible to put quotas on the filesystem, third, it is possible to disable setuid/setgid
programs on the mount. It is even possible to disable execute - though that can cause
problems for some strange applications - those that dynamically create/compile/execute
programs based on user configuration or direction.
The security on /tmp comes from the sticky bit (1000 - the 1 in 1777). It prevents users
from renaming or deleting files that they don't own. SELinux reinforces that with
Using a symbolic link for /tmp is not a good idea. When the system first boots /tmp must
be available for workspace for various utilities used during the boot. It is the designated
workspace when the root is truly read only (as in CD/DVD live systems, or routers,...)
when memory is used for /tmp. Another problem with a symbolic link is that the directory
tree containing the linked to directory must at a minimum be x (executable, though in
this case x means searchable). It also bypasses the SELinux enforcement, and the
linked to directory must be 1777.