Thank you to RTL-SDR.COM reader Steve Hagerman for writing in and sharing his Python script that allows SDR++ users to convert a CSV file of frequency bookmark information into a JSON file that SDR++ recognizes. Steve explains:

[In SDR++] one of the biggest issues is in making frequency bookmarks. SDR++ uses a JSON file to store frequency bookmarks which is hard to edit manually. While there is a direct means to enter bookmarks directly in SDR++, it is tedious and requires too many mouseclicks.

To fix this I wrote a Python script to take easily made XLSX Spreadsheet of frequencies to convert to a JSON file that can be used directly with SDR++.