import re
text = """ID        Information

1         :20:Test1  :25:test2:28C:test3"""

valid_line_rx = r'^(\d+\s*)(:\d{2}[A-Za-z]?:.*)'
print( re.sub(valid_line_rx, lambda m:
  "\n".join(["{}{}".format(m.group(1),x) for x in re.split(r'(?!^)(?=:\d{2}[A-Za-z]?:)', m.group(2))]),
  text, 
  flags=re.M)
)