function StringChangeEx(var S: String; const FromStr, ToStr: String; const SupportDBCS: Boolean): Integer;

Changes all occurrences in S of FromStr to ToStr. If SupportDBCS is True (recommended unless you require binary safety), double-byte character sequences in S are recognized and handled properly. Otherwise, the function behaves in a binary-safe manner. Returns the number of times FromStr was matched and changed.

When working with strings containing paths or filenames, be sure to pass True in the SupportDBCS parameter. Otherwise, paths with Chinese, Japanese, or Korean characters may be corrupted.

var
  S: String;
begin
  S := ExpandConstant('{commonappdata}');
  // S = 'C:\Documents and Settings\All Users\Application Data'

  StringChangeEx(S, '\', '/', True);
  // S = 'C:/Documents and Settings/All Users/Application Data'
end;