procedure FileReplaceString(const FileName, searchstring, replacestring: string);
var
fs: TFileStream;
S, N: string;
begin
fs := TFileStream.Create(FileName, fmOpenread or fmShareDenyNone);
try
SetLength(S, fs.Size);
fs.ReadBuffer(S[1], fs.Size);
finally
fs.Free;
end;
N := StringReplace(S, SearchString, replaceString, [rfReplaceAll, rfIgnoreCase]);
fs := TFileStream.Create(FileName, fmCreate);
try
fs.WriteBuffer(N[1], Length(N));
finally
fs.Free;
end;
end;