diff --git a/generate_act_format.py b/generate_act_format.py
index 538286f..0f50f75 100644
--- a/generate_act_format.py
+++ b/generate_act_format.py
@@ -36,7 +36,7 @@ def generate_act_format(opcodes_file):
   opcode_mapping = dict()
 
   for line in opcodes_file.readlines():
-    match_groups = re.findall(r'^\s*([^\/].*)= (.*),\s*\/\/.*$', line)
+    match_groups = re.findall(r'^\s*([^\/].*)=\s*(.*),\s*\/\/.*$', line)
     if len(match_groups) != 1:
       continue
 
diff --git a/generate_opcodes_file.py b/generate_opcodes_file.py
new file mode 100644
index 0000000..86bbc6c
--- /dev/null
+++ b/generate_opcodes_file.py
@@ -0,0 +1,61 @@
+import json
+import re
+import click
+
+def load_diff_file(f, reverse=False):
+  diff = dict()
+  diff_json = json.load(f)
+  for pair in diff_json:
+    if "old" not in pair or "new" not in pair:
+      continue
+    old_key = "new" if reverse else "old"
+    new_key = "old" if reverse else "new"
+    for old_opcode in pair[old_key]:
+      diff[int(old_opcode, 16)] = set((int(new_opcode, 16) for new_opcode in pair[new_key]))
+  return diff
+
+def opcodes_str(opcodes):
+  if len(opcodes) == 1:
+    return hex(list(opcodes)[0])
+  elif len(opcodes) > 1:
+    return " or ".join((hex(opcode) for opcode in opcodes))
+  else:
+    return "UNKNOWN"
+
+def replace_line_with_new_opcode(line, diff, ver):
+    match_groups = re.findall(r'^\s*([^\/].*)=\s*(.*),\s*\/\/.*$', line)
+    if len(match_groups) != 1:
+      return line
+
+    opcode_name = match_groups[0][0]
+    opcode_val = match_groups[0][1]
+    if " or " in opcode_val:
+      old_opcode = int(opcode_val.split(" or ")[0], 16)
+    else:
+      old_opcode = int(opcode_val, 16)
+    if old_opcode in diff:
+      new_opcodes = diff[old_opcode]
+      return f"{opcode_name}= {opcodes_str(new_opcodes)}, // updated {ver}\n"
+
+    return f"// {line}"
+
+
+@click.command()
+@click.argument("new_version_string")
+@click.argument("diff_file", type=click.File('r'))
+@click.argument("opcodes_file", type=click.File('r'))
+@click.option("--reverse", is_flag=True)
+def generate_opcodes_file(new_version_string, diff_file, opcodes_file, reverse):
+  diff = load_diff_file(diff_file, reverse)
+  queued_lines = []
+  for line in opcodes_file.readlines():
+    queued_lines.append(replace_line_with_new_opcode(line, diff, new_version_string))
+
+  new_filename = f"{new_version_string}_opcodes.txt"
+  with open(new_filename, "w+") as f:
+    f.writelines(queued_lines)
+
+  print("Wrote to", new_filename)
+
+if __name__ == "__main__":
+  generate_opcodes_file()
\ No newline at end of file