In the macro page manual (https://developer.steinberg.help/display/HMP/Text) it is said that the read only feature is in Halion 6.1.
This version of Halion 6 does not exist. If you go to the download page the most recent version of Halion is 6.0.15. (https://www.steinberg.net/index.php?id=downloads_halion_6&L=1).
The most current version of H6 does not have this property.