shallow copy tree before write_to

and deep copy key/values that will be modified

asdf/asdf.py

@@ -1362,12 +1362,14 @@ def write_to(
                 ignore_unrecognized_tag=self._ignore_unrecognized_tag,
                 ignore_implicit_conversion=self._ignore_implicit_conversion,
             )
-            naf._tree = self.tree  # avoid an extra validate
-            pre_write_tree = {}
+            naf._tree = copy.copy(self.tree)  # avoid an extra validate
+
+            # deep copy keys that will be modified during write
             modified_keys = ["history", "asdf_library"]
             for k in modified_keys:
                 if k in self.tree:
-                    pre_write_tree[k] = copy.deepcopy(self.tree[k])
+                    naf._tree[k] = copy.deepcopy(self.tree[k])
+
             # copy over block storage and other settings
             block_to_key_mapping = {v: k for k, v in self._blocks._key_to_block_mapping.items()}
             # this creates blocks in the new block manager that correspond to blocks
@@ -1393,10 +1395,6 @@ def write_to(
                     blk._used = True
                     blk._data_callback = b._data_callback
             naf._write_to(fd, **kwargs)
-            for k in modified_keys:
-                if k in self._tree:
-                    del self._tree[k]
-            self._tree.update(pre_write_tree)
 
     def _write_to(
         self,