ATN files are not scripts, they are generally best edited in the Photoshop Action panel. Simply add a new text layer action step, then delete the old one (ensuring that all other options are the same).
Another approach would be to record the selection of the text layer and the changing of the old text to the new text (2 extra steps).
That being said, it should be possible to do what you are looking for with the use of special tools:
2. Edit burgers to chicken in the XML file
I personally would work on duplicated files, remove out all other steps and then only copy the new step into the old action via the Action panel, rather than converting the entire action to XML and back to an action (keep it simple and translate/edit as little as possible).
I just recorded two steps action where I 'Make text layer with a text "bobs burgers", 'Set current text layer' setting new text to "bobs chicken". I don't know why, but if name of your 2nd step is exact, then 'using text layer' in my case it's 'Set current text layer'. Third step I have no idea you state as a step or just info or text layer's content. Anyway if you want to edit 'Set current text layer' step or however you name it, just choose manually "bobs burgers" layer from Layers panel, then switch panels (if not visible) to Actions panel and double left mouse click on 'Set current text layer'. It'll highlight that layer in your document that you only type in "bobs chicken" and press enter. Your 'Set current text layer' step is rerecorded, and now when you play your action from start it will give changed name. You may click action Set that contains action with that step, then in upper right corner open dropdown list and select 'Save Actions...' to disk. Upload your action to post if that doesn't solve problem.
Photoshop Script are Programs written in a language and intrepid by Photoshop Scripting Plug-in. You can use logic. Actions are recorded Photoshop steps you record, edit and play in the Action Palette. Action steps are hard wired no logic can be use in action except for a few condition of document and layers that are supported by the action recorder. Therefore it is very hard to deal with size in actions. If all you document are the same size and resolution you can record steps to add text. However If you want you able to use your action with any document you will find you need to use different size text for different document sizes. Creating action that will work on most document require knowledge and a well design process.
Crafting Actions Package UPDATED Aug 10, 2014 Added Conditional Action steps to Action Palette Tips
- Action Actions Palette Tips.txt
- Action Creation Guidelines.txt
- Action Dealing with Image Size.txt
- Action Enhanced via Scripted Photoshop Functions.txt
- CraftedActions.atn Sample Action set includes an example Watermarking action
- Sample Actions.txt Photoshop CraftedActions set saved as a text file.
- More then a dozen Scripts for use in actions