Summary I'd like to request support for assigning custom metadata — such as unique IDs or arbitrary key-value pairs — directly to individual cells in Excel using the Office.js API. Why This Matt...
Could you not use EntityCellValue interface? https://learn.microsoft.com/en-us/javascript/api/excel/excel.entitycellvalue?view=excel-js-preview
https://learn.microsoft.com/en-us/office/dev/add-ins/excel/excel-data-types-entity-card