Convert to pdf/a with libreoffice online Rest service

I started the docker image “libreoffice/online”, after adjusting the “loolwsd.xml” to allow my ip I am able to convert documents by using:

curl --insecure -F “data=@TestDocument.docx” https://localhost:9980/lool/convert-to/pdf > TestDocument.pdf

The result is a 1.5 compatible PDF. Next step (for me) is the create a PDF/A compatible pdf.

I read that I need to change the filter options “SelectPdfVersion” to 1. In the file “registrymodifications.xcu”, but I cannot find that file. Maybe it only applies to libreoffice (not online).
It looks like Jodconverter adds filteroptions with the prefix fd to the request. But trying something like https://localhost:9980/lool/convert-to/pdf?fdSelectPdfVersion=1 did not work for me.

In LOOLWSD.cpp I see that the saveAs message always ends with an empty options: “options=”.

Is there a way to change the settings for a document conversion?