diff -Nuar samba4-4.0.0~alpha17~git201110100928.orig/source4/scripting/python/samba/join.py samba4-4.0.0~alpha17~git201110100928/source4/scripting/python/samba/join.py
--- samba4-4.0.0~alpha17~git201110100928.orig/source4/scripting/python/samba/join.py	2012-07-04 08:28:59.000000000 +0200
+++ samba4-4.0.0~alpha17~git201110100928/source4/scripting/python/samba/join.py	2012-07-04 08:30:11.000000000 +0200
@@ -212,10 +212,10 @@
                                attrs=["msDS-krbTgtLink", "userAccountControl", "serverReferenceBL", "rIDSetReferences"])
         if len(res) == 0:
             raise Exception("Could not find domain member account '%s' to promote to a DC, use 'samba-tool domain join' instead'" % ctx.samname)
-        if "msDS-krbTgtLink" in res[0] or "serverReferenceBL" in res[0] or "rIDSetReferences" in res[0]:
-            raise Exception("Account '%s' appears to be an active DC, use 'samba-tool domain join' if you must re-create this account" % ctx.samname)
-        if (int(res[0]["userAccountControl"][0]) & (samba.dsdb.UF_WORKSTATION_TRUST_ACCOUNT|samba.dsdb.UF_SERVER_TRUST_ACCOUNT) == 0):
-            raise Exception("Account %s is not a domain member or a bare NT4 BDC, use 'samba-tool domain join' instead'" % ctx.samname)
+        # if "msDS-krbTgtLink" in res[0] or "serverReferenceBL" in res[0] or "rIDSetReferences" in res[0]:
+        #     raise Exception("Account '%s' appears to be an active DC, use 'samba-tool domain join' if you must re-create this account" % ctx.samname)
+        # if (int(res[0]["userAccountControl"][0]) & (samba.dsdb.UF_WORKSTATION_TRUST_ACCOUNT|samba.dsdb.UF_SERVER_TRUST_ACCOUNT) == 0):
+        #     raise Exception("Account %s is not a domain member or a bare NT4 BDC, use 'samba-tool domain join' instead'" % ctx.samname)
         
         ctx.promote_from_dn = res[0].dn
 
diff -Nuar samba4-4.0.0~alpha17~git201110100928.orig/source4/scripting/python/samba/netcmd/domain.py samba4-4.0.0~alpha17~git201110100928/source4/scripting/python/samba/netcmd/domain.py
--- samba4-4.0.0~alpha17~git201110100928.orig/source4/scripting/python/samba/netcmd/domain.py	2012-07-04 08:28:59.000000000 +0200
+++ samba4-4.0.0~alpha17~git201110100928/source4/scripting/python/samba/netcmd/domain.py	2012-07-04 08:29:54.000000000 +0200
@@ -155,6 +155,9 @@
         Option("--domain-critical-only",
                help="only replicate critical domain objects",
                action="store_true"),
+        Option("--promote-existing",
+               help="keep the SID during join",
+               action="store_true"),
         Option("--machinepass", type=str, metavar="PASSWORD",
                help="choose machine password (otherwise random)")
         ]
@@ -188,13 +191,13 @@
             join_DC(server=server, creds=creds, lp=lp, domain=domain,
                     site=site, netbios_name=netbios_name, targetdir=targetdir,
                     domain_critical_only=domain_critical_only,
-                    machinepass=machinepass)
+                    machinepass=machinepass, promote_existing=True)
             return
         elif role == "RODC":
             join_RODC(server=server, creds=creds, lp=lp, domain=domain,
                       site=site, netbios_name=netbios_name, targetdir=targetdir,
                       domain_critical_only=domain_critical_only,
-                      machinepass=machinepass)
+                      machinepass=machinepass, promote_existing=True)
             return
         elif role == "SUBDOMAIN":
             netbios_domain = lp.get("workgroup")