Think about this; normally, the default perms on /var, /opt are correct. Think about what you are trying to accomplish, do you really need to mess with them?
If you want an area where people can share files, then the usual approach is
1. create newuser, newgrp
2. create the home dir for newuser, newgroup
3. chmod g+s newgrp newdir
4. add newgrp to reqd users as a 2ndary group
If(!) you need to go into even more fine-grained ctrl, then add ACLs to the above.
Note that the
mount -o remount,acl /newdir
can be done on the fly, ie no reboot reqd. See also tune2fs eg
tune2fs -l |grep options
will show if acls are already turned on.
Why exactly would you want to mess with /var, /opt?