Here's how DPP3 and DPP4 store recipes in CR2 files, for those who are interested. This post is purely informational, as I haven't found the tool to automate this process yet.
You will need a fairly recent version of exiftool to run some of the examples. DO NOT run any of the commands modifying images against your actual images. Use a throw-away copy for experimentation.
Both versions of DPP store recipes in EXIF tags, under CanonVRD. DPP3 and DPP4 tags are mixed in and some have the same names and some do not.
Here's how you can see all recipe tags:
exiftool -s -a -G -H -CanonVRD:all _MG_2280.CR2
I will demonstrate DPP3 vs. DPP4 tags using RAW brightness value. If image RAW brightness value was changed in both, DPP3 and DPP4, this command will show two brightness values.
exiftool -s -a -G -H -CanonVRD:RawBrightnessAdj _MG_2280.CR2
[CanonVRD] 0x20001 RawBrightnessAdj : 1.25
[CanonVRD] 0x0038 RawBrightnessAdj : 2.00
The top one is for DPP4 and the bottom is for DPP3. Notice how they have the same name and different tag IDs. This means that some of the scripts circulating online may not work as intended if just the tag name is used to set the value.
Here's an example how I can take the DPP3 value and apply it against the image, so DPP4 will show the desired brightness, which in this case is 2.0.
exiftool -CanonVRD:ID-0x20001:RawBrightnessAdj=2.00 _MG_2280.CR2
If you have DPP4 open in this directory, you will see brightness jump up immediately after this command.
Tag names don't always match between DPP3 and DPP4. For example, crop tag names for DPP3 look like this.
[CanonVRD] 0x0246 CropLeft : 684
[CanonVRD] 0x0248 CropTop : 726
[CanonVRD] 0x024a CropWidth : 3417
[CanonVRD] 0x024c CropHeight : 2278
, while crop tag names for DPP4 look like these.
[CanonVRD] 0x0003 CropX : 100
[CanonVRD] 0x0004 CropY : 100
[CanonVRD] 0x0005 CropWidth : 3877
[CanonVRD] 0x0006 CropHeight : 2585
DPP4 recipes saved as standalone files are stored as EXIF values as well, so you can see all DPP4 tag values if you run the same command against a .dr4 file, like this.
exiftool -s -a -G -H -CanonVRD:all _MG_2280.dr4
You can see a full list of Canon VRD tags and meanings of some values on this page.
https://exiftool.org/TagNames/CanonVRD.html
Update 2022-12-19
Posted a thread on exiftool forums on why JSON export/import fails. JSON may be used to extract DPP3 values, remapped into using DPP4 tag IDs and then imported into .CR2 images.
https://exiftool.org/forum/index.php?topic=14288.0
This is work in progress. I will keep updating this post if anything interesting surfaces in my search, because Canon forums are messy in how they present threads.
