Cortar Cadena de texto envuelta en etiqueta html

[opzina]

Tengo un párrafo como el siguiente:

Código HTML:

<p>
[B]Lorem Ipsum[/B] is simply dummy text of the printing and  typesetting industry. Lorem Ipsum has been the industry's standard dummy  text ever since the 1500s, when an unknown printer took a galley of  type and scrambled it to make a type specimen book. It has survived not  only five centuries, but also the leap into electronic typesetting,  remaining essentially unchanged. 
</p>
 

Al cortarlo a la mitad, necesitaría que cada parte este envuelta con la misma etiqueta de origen, en este caso <p>