How to insert text in some fields of a .xlsx spreadsheet file?

Hi all! I have a formatted .xlsx-file (as template) in which I need to insert some text in given fields before enabling for download (through Phoenix), and so I’m looking for a package that can do that. I’ve searched at hex, but most of them seem to only do either parsing or writing. It doesn’t necessarily need to be .xlsx but from what I know about for example .csv those don’t handle formatting.

Are you aware of any package suitable for this?
Or do you have experience in working with .xlsx and know how much effort it would take for me to write the modules on my own?

The MS-XLSX standard is here.

I don’t have experience, but my first attempt would be to try to create “snip points” in the xlsx file and just use plain EEX templates to make the necessary changes/insertions.

Thanks! What do you mean by snip points?

Unique markers like BLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAH, just anything that won’t ever normally show up, then just replace those.