1. Copy $env/templates/site.html.sample -> $env/templates/site.html
2. Add the following snippet to site.html
<py:match path="//div[@id='content' and @class='ticket']//label[@for='field-summary']">
<label for="field-summary">Task:</label>
</py:match>
There may be a way to change the selector to directly select the text node, which would avoid having to recreate label node. For example,
<py:match path="//div[@id='content' and @class='ticket']//label[@for='field-summary']/???">
Task:
</py:match>
where the ??? is replaced with the appropriate selector. I'm not very fluent with XPath. If someone knows how to do this, I'd be interested to learn.
The interface customization is very powerful, you basically just need a quick intro to Genshi directives and a good grasp of XPath.