As the hlshd mode is no longer available for download for most programmes I would like to request an option be included in get_iplayer to remux 50fps files to 25fps.
Failing that could someone post detailed step by step instructions on how to remux files downloaded using the  --raw option to 25fps and then add the the metatdata.
Thanks.

A definite no from me, and I won't accept pull requests for this. This is a red line for me, I'm afraid. Too many variables and too much trouble to support, for too little benefit. You can already do whatever you like with --command. And you're not obligated to use --raw. For example, ffmpeg can copy metadata when re-encoding from MP4 to MP4, and ffmpeg 4.0+ can even copy the thumbnail, so you may decide that extra post-processing by get_iplayer is worth it. Only you can decide on such trade-offs, and only you can decide how you want to re-encode files.

I've copied this thread to off-topic forums if anyone else wants to reply to your request for instructions. Any further comments should go there. This thread is closed.