You can't edit a .SEQ file directly (unless you can read the raw code) - you should import it, edit the action with Acrobat then re-export it.
Actions don't have any logic so you cannot do what you want with the inbuilt steps. It's only possible with JavaScript - you don't need extra software (beyond Acrobat) but if you've never written a JS program it's not a trivial thing to work out.
Someone might reply with a working code sample, but the general logic would be:
- Loop through each page and find the rotation using the getPageRotation() function. Also get the page dimensions using getPageBox() as the page may be 'true' landscape or it may be a portrait page with a 90-degree rotation applied.
- Go through the array of values and find the ones which need to be turned. Rotate them using setPageRotations().
- Count the pages of each type and use newPage() to insert your blank page in the right place.
To run this against a whole bunch of documents you'd create a new Action, use the "JavaScript" step, put in the code and save it. Note that the JS step cannot tell the Action if the file has been changed or not, so every file you process will have to be re-saved.
