There is no way with samba4 to force samba4 to reload the configuration so in order to add a share samba must restarted everytime.
Yeah, in SAMBA 3 we have working the addition of shares dynamically during the server runtime (through RPC calls and registry backend). Sometime, we should also have something like this in SAMBA 4, I agree.
Mark as "Feature request".
Let us mark this as duplicate of 7375 since the feature you describe is to be implemented by "smb.conf" reloading.
*** This bug has been marked as a duplicate of bug 7375 ***