I'm not completely clear on what you're trying to do, but there is no bodytext placeholder unless you've created one.
If the text you're trying to change is all in the content field of the resource, putting this in your Template where the content tag is might work:
[[*content:replace=`One==Two`]]
If you want that to be context-sensitive, you could use a Context Setting containing `One===Two` and use this for the content tag:
[[*content:replace=[[++ContextSettingName]]]]
If some words you need to replace are not in the 'content' field, you could create a plugin with custom code to do the replacements.
Another way to go would be to make all the words that need replacing into either language tags, placeholder tags, or Setting tags. Using Setting tags would be the most straightforward.
For example, use a Setting tag like this:
And a Context Setting with a key of someWord and a value that's what you want to replace the tag with.