Hello,
sorry for the late reply. There is no separate list yet, but the keys for -profileParam are the same as the values of a user profile in the registry, as you assumed. They override the values of any profile, also of a built-in one.
That pdf-standard did not work with a built-in profile was a bug: the PDF/A conversion failed when no PDF/A color profile was given. This is fixed since version 11.31.0. With the current version this works:
"C:\Program Files\PDF24\pdf24-DocTool.exe" -applyProfile -profile default/best -profileParam pdf-standard a-2 -silent -outputFile "C:\out\file.pdf" "C:\in\file.pdf"
Possible values for pdf-standard are a-1, a-2, a-3, a-4 and a-4f (PDF/A), x-3 (PDF/X-3) and 1.2 to 1.7. With -silent (also since 11.31.0) no window is shown; errors are reported via the exit code.
Details in the manual:
Single files can also be converted online: https://tools.pdf24.org/en/pdf-to-pdfa