A minor revision to stix2.versioning: it's silly to look up a

class in the registry when you have an instance of one of those
classes.  Because in that case, you can just get the class of the
instance and not deal with the registry at all.

stix2/versioning.py

@@ -168,11 +168,15 @@ def new_version(data, allow_custom=None, **kwargs):
     # across versions.
     sco_locked_props = []
     if is_sco(data, "2.1"):
-        cls = stix2.registry.class_for_type(
-            data["type"], stix_version, "observables"
-        )
         uuid_ = uuid.UUID(data["id"][-36:])
         if uuid_.variant == uuid.RFC_4122 and uuid_.version == 5:
+            if isinstance(data, stix2.base._Observable):
+                cls = data.__class__
+            else:
+                cls = stix2.registry.class_for_type(
+                    data["type"], stix_version, "observables"
+                )
+
             sco_locked_props = cls._id_contributing_properties
 
     unchangable_properties = set()