diff --git a/docs/syntax.md b/docs/syntax.md
index 005883a..ce532b0 100644
--- a/docs/syntax.md
+++ b/docs/syntax.md
@@ -347,7 +347,8 @@ Alternatively items can be added to just the BOM by putting them in the section
     <str>:  # leading string of .gv entry
       <str> : <str>  # attribute and its new value
       # Any number of attributes can be overridden
-      # for each entry
+      # for each entry. Attributes not already existing
+      # in the entry will be appended to the entry.
 
   append: <str/list> # string or list of strings to append to the .gv output
 ```
diff --git a/src/wireviz/Harness.py b/src/wireviz/Harness.py
index 548a687..8e5a7f3 100644
--- a/src/wireviz/Harness.py
+++ b/src/wireviz/Harness.py
@@ -367,11 +367,16 @@ class Harness:
                     keyword = match and match[2]
                     if keyword in self.tweak.override.keys():
                         for attr, value in self.tweak.override[keyword].items():
+                            # TODO?: If value is None: delete attr?
                             if len(value) == 0 or ' ' in value:
                                 value = value.replace('"', r'\"')
                                 value = f'"{value}"'
-                            # TODO?: If value is None: delete attr, and if attr not found: append it?
-                            entry = re.sub(f'{attr}=("[^"]*"|[^] ]*)', f'{attr}={value}', entry)
+                            entry, n_subs = re.subn(f'{attr}=("[^"]*"|[^] ]*)', f'{attr}={value}', entry)
+                            if n_subs < 1:
+                                # If attr not found, then append it
+                                entry = re.sub(r'\]$', f' {attr}={value}]', entry)
+                            elif n_subs > 1:
+                                print(f'Harness.create_graph() warning: {attr} overridden {n_subs} times in {keyword}!')
                         dot.body[i] = entry
 
         if self.tweak.append is not None: