I see that /bin/tar is part of advcomp.tce and the rest is in /usr/local/bin. /usr/local/bin and /usr/local/sbin are at the front of $PATH and will be the programs used even if the same one exists in /bin, /sbin, /usr/bin, /usr/sbin. GNU tar can be placed in /usr/local/bin and it will be the tar used instead of the busybox one; no need to overwrite busybox links, just place the gnu or other apps in /usr/local/(s)bin. This makes it easy to either use or revert to busybox commands when "real" ones are installed in /usr/local, just delete the one in /usr/local/bin or use the command "busybox tar". The need to overwrite system commands is greatly reduced by /usr/local/bin being at the front of the PATH.
TCZ's don't overwrite existing files or symlinks and thus busybox tar is not overwritten by the tcz.