DSBWrtSysctl is a FreeBSD® command-line tool to add variable=value pairs to /etc/sysctl.conf, or to change the values of existing variables.
0.1.5
# cd /usr/ports/sysutils/dsbwrtsysctl && make install distclean
# tar xf dsbwrtsysctl-0.1.5.tgz && cd dsbwrtsysctl-0.1.5 && make install