How to append / prepend into a rich text field
If you want to prepend another paragraph you could to this:

{% set paragraphs = entry.body|split('&lt;/p&gt;') %}
{% for paragraph in paragraphs %}
  {% if loop.index == 1%}
    &lt;p&gt;Prepended Custom Text&lt;/p&gt;
  {% endif %}
    {{paragraph|raw}}
{% endfor %}


If you want to display a custom string in the first paragraph itself you could do this:

{% set paragraphs = entry.body|split('&lt;/p&gt;') %}
{% for paragraph in paragraphs %}
  {% if loop.index == 1%}
    {% set paragraph = paragraph|replace({'&lt;p&gt;': '&lt;p&gt;My custom prepended Text '}) %}
  {% endif %}
    {{paragraph|raw}}
{% endfor %}


This looks a little bit hacky tough there are probably prettier ways to do so.