My environment: Windows-11; PDFsam 5.3.1; a few .json files for "merge" projects.
In Windows, a general convention with mainstream applications is that "click on data file" starts the application, using that file as its data input, and based on the extension of the data file. Example: click on .docx opens MS Word (or LibreOffice Writer. etc.); click on .pdf opens Adobe Reader (or similar).
Could PDFsam similarly support being associated with a .json extension, and open that file as its workspace?