I'll answer my own question. You can create a User Library Field and choose a Calculated Data Expression and choose FileKey(). So now in my Playlist that I use for Export I can include the FileKey and then use that value when updating the Library thru the MC API REST interface.
SetInfo
Set information about a file object.
Parameters:
File: The key of the file. (default: -1)
FileType: The type of value provided in 'File' (Key: file key; Filename: filename of file). (default: Key)
Field: The field to set. (default: )
Value: The value to set the field to. (default: )
List: Set to 'CSV' and comma delimit (RFC 4180) the field and value to set multiple values in one call. (default: )
Formatted: Set to 1 if you're passing a formatted value (like a formatted date). (default: 1)
Response:
Examples:
Click here
This is an example URL to update File 343079 with Tempo value.http://192.168.1.100:52199/MCWS/v1/File/SetInfo?File=343079&FileType=Key&Field=tempo&Value=100&Formatted=1You also have to authenticate with username and password. That can be done by getting a token.
Authenticate
Simple query to test and establish authentication.
Response:
Token: The token that can be appended to calls in place of HTTP authentication.
ReadOnly: Whether the token is for read-only access. If not present or false, the token has full rights.
PreLicensed: True if MC is running in restricted mode
Examples:
Click here
http://192.168.1.100:52199/MCWS/v1/Authenticate<Response Status="OK">
<Item Name="Token">2Kb7FzP5</Item>
<Item Name="ReadOnly">0</Item>
<Item Name="PreLicensed">0</Item>
</Response>