root@freebsd:/root # pw groupmod wheel -m test

root@freebsd:/root # cat /etc/group | grep test
wheel:*:0:root,neo,test
test:*:1002:
		

root@freebsd:/root # pw usermod test -g wheel

root@freebsd:/root # cat /etc/passwd | grep test
test:*:1002:0:test:/home/test:/bin/csh
		

或者直接修改/etc/group文件，把相应的用户加到wheell组就可以

wheel:*:0:root,username