[ecfisa]

hola yossi.

Usá la propiedad Paragraph del TRichEdit.

Ejemplo:

 
procedure TForm1.ComboBox1Change(Sender: TObject);
begin
  case ComboBox1.ItemIndex of
    0:RichEdit1.Paragraph.Alignment:= taLeftJustify;
    1:RichEdit1.Paragraph.Alignment:= taRightJustify;
    2:RichEdit1.Paragraph.Alignment:= taCenter;
  end;
end;

En cuanto a tipo, color, estilo, etc.
Podes hacer por ejemplo:

procedure TForm1.Button1Click(Sender: TObject);
begin
  if FontDialog1.Execute then
  begin
    RichEdit1.SelAttributes.Color:= FontDialog1.Font.Color;
    RichEdit1.SelAttributes.Style:= FontDialog1.Font.Style;
    RichEdit1.SelAttributes.Name:= FontDialog1.Font.Name;
    RichEdit1.SelAttributes.Size:= FontDialog1.Font.Size;
  end;
end;

Saludos