Slightly off topic, but a little bit related, so I ask here:
I stared making something similar (but because of COVID 19 it has been delayed at least a year).
For this, I planned to have a few extra fields for the users (that had to register), with ONE field that can only be edited by 'admins' ( a BOOL field to check if they got their T-shirt').
Is this doable with memberdata.xml (or another profile/xml file) ?
So it looks like it has to be done in userschema.xml
Does not seem to work, the user can still edit the field
<field name="tshirt" type="zope.schema.Bool" users:forms="On Registration|In User Profile"