Replace char occurrences

Get a string from a given string where all occurrences of its first char
have been changed to ‘$’, except the first char itself.
Sample String :
‘restart’
Expected Result :
‘resta$t’
def change_char(S):
  char = S[0]
  S = S.replace(char, '$')
  S = char + S[1:]
  return S

# test
print(change_char('restart'))          # resta$t