Replacing a field in a dump file with the equivalent field from another dump file

Hello, I want to replace the soil moisture field from the start dump of one of our simulations (u-ds882), which uses UM vn13.0, with the start dump from another simulation (bb055) which used vn10.8. I’m having problems converting these files into netcdf and back cleanly (using cfa), so I’m not able to use xarray or nco to edit, which would be my preferred tools. I think I need to modify the files directly but I have very little experience with Met Office file formats.

What would be the recommended tool(s) to do this? Reading online, it seems like mule and iris are the main tools, maybe cf-python - which would be better for this task?

Does anyone have any scripts which do something similar, they are happy to share? Or point in the direction of some training example scripts which do something similar?