Figured it out and it seems to work. I need to do more testing.
As you said, use Adobe DNG converter to convert Sony A1 ARW files to DNG.
Then run EXIF Tool to change the camera model from “ILCE-1” to “ILCE-7MR4”.
Viola… Done…
In Windows, paste this into a batch file. Then drag a directory full of DNG files onto it. It will update the camera model appropriately. The options specify it will only process DNG files (it won’t modify your original ARWs) and it will only modify files where the camera model is ILCE-1. And it overwrites existing files in place (as you have the ARW for backup.)
Hope it helps. Here’s the text to drop in the batch file.
“C:\FILL_IN_YOUR_PATH_HERE\Exiftool.exe” -Model=“ILCE-7RM4” -ext DNG -overwrite_original -if “$Model eq ‘ILCE-1’” %*