KB: Convert Plated via Backdrills to Non-Plated in ODB++ output

Solution Details

First, check with your fabricator. They may prefer to make the changes for you.
However, if you need to change the VIA type to NON-PLATED, this shows you how to determine which Drills need to be modified and to which files changes are required.

In the generated ODB export folder, via types are defined in a file named Tools.
These are contained in a Drill folder corresponding to the drill range.  

The Drill folders are named Drill#, where # is a sequential integer numbering of each folder (except the first is just named Drill). Drill folders are located here: 

<path>\odb\steps\pcb\layer\Drill*

To determine which Tools files need editing, it is necessary to examine the Drill pair definitions in the Matrix file here:

<path>\odb\matrix\matrix\matrix

Edit the matrix file in a text editor. For the Drill layers, the "Layer{}" section will contain a Type=Drill, and Name= and list the start and end names. Backdrills have an extra property called ADD_TYPE=BACKDRILL, which makes it easier to determine which Drill names you will need to modify.

For example:
LAYER {
    ROW=25
    CONTEXT=BOARD
    TYPE=DRILL
    NAME=DRILL1
    POLARITY=POSITIVE
    START_NAME=_L01__TOP_LAYER
    END_NAME=_L03__SIGNAL
    OLD_NAME=
    ADD_TYPE=BACKDRILL
}

Here, the Drill has a name of DRILL1, and this will be the corresponding folder name in the Layer folder.
Make a list of all the Drill name for the LAYER {} that contain BACKDRILL ADD_TYPE

To modify the corresponding tool file, you would edit the tools file here:

<path>\odb\steps\pcb\layer\Drill1\tools

In the tools file, it is necessary to change the Via Type to Non_Plated.

E.g., Edit the file, find:

    TYPE=VIA

and change to:

    TYPE=NON_PLATED
    
Take care to only change Blind Vias that are back drills, as determined earlier.