[ecfisa]

Hola Angel.

void StyledText(TRichEdit *RE, AnsiString Searched, TFontStyle FS)
{
  RE->SelStart = RE->FindText(Searched,0,RE->GetTextLen(), 
    TSearchTypes() << stMatchCase);
  RE->SelLength = Searched.Length();
  RE->SelAttributes->Style = RE->SelAttributes->Style << FS;
}

Ejemplo de uso:

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  RichEdit1->Text = "negrita, italica, subrayada, tachada";
  StyledText(RichEdit1, "negrita", fsBold);
  StyledText(RichEdit1, "italica", fsItalic);
  StyledText(RichEdit1, "subrayada", fsUnderline);
  StyledText(RichEdit1, "tachada", fsStrikeOut);
  QRRichText1->ParentRichEdit = RichEdit1;
  QuickRep1->Preview();
}

Saludos