any way to convert captions to transcription

Would it be an option to re-transcribe the sequence? (right-click on the sequence / Re-Transcribe)

There is a way to convert your subtitles back to a transcript, and then create CEA-608 captions from that - it's a bit of a workaround, but bear with me.

1. Add your captions file to your timeline

2. In the Text panel, choose Captions > Export > Export to Text File

3. Open the text file in a Text editor. There are two things that need to change about this format - you need a speaker name under each timecode line, and you need to remove any line breaks in the dialogue. You can do this manually, or use something like ChatGPT to do this automatically with a command like "This is a subtitle text file. Add the name of the speaker 'Unknown' under each line of timecode and remove any line feeds in the dialogue."

4. If you're timeline is not a single clip, export it as an audio file and then re-import it into your project

5. Load this audio file or your single clip into the Source monitor 

6. In the Text panel, choose Transcript > Import > Import Corrected Transcript
7. If you exported an audio file in step 4, add this to your timeline
8. In the Text panel, choose Transcript > Create Captions and choose the CEA-608 format. 

Hope this helps!

Why not just recreate the captions as CEA-608?