What exactly does /msg NickServ SET GUARD ON do?
If you mean changes your nick for not identifying, that would be /msg NickServ SET KILL ON and in the current devel release is enabled as a default option on registration (NSDefKill), but also by default a mask is added to the nicks access list in NickServ to prevent the person who registers the nick, from being Guest'ed which can in the current devel version be disabled by putting a # in front of NSAddAccessOnReg. But thats only in 1.7.* series and beyond.