On registration I want the user to give an email address that complies to a regular expression restriction (not only domain). This address will be verified by sending an email to it. The user will then be added to the "Member" group.
CB already does this. Enable registration confirmation and edit your email field to add custom REGEX validation to it. You can even use our CB Reconfirm Email plugin to force them to confirm any email changes in profile edit too so they always are using a valid email address.
Later, the user may modify this address to any valid address.
But I want to keep the registration address in a readonly field.
I don't understand. How are they going to supply an email address if it's read only. Read only fields are still editable at registration, but are not at profile edit.
1°) May I do a copy of the email field to the readonly field with some other plugin that controls the registration form while the user fills it (I forgot the name of that plugin)
You copy the value of 1 field to another using a Field action in CB Auto Actions on the after registration and/or after profile update triggers.
2°) should I use "CB Auto Action" to UPDATE ##_comprofiler just after registration in order to SET the readonly to be equal to the email field ?
No, use a Field action.
3°) or rely on DomainRestriction Joomla Extension for 1°) (does 99% of the work)
plus "Auto Group for Community Builder" for 2°) (with a little hack).
Just use edit your Email field and add whatever REGEX validation you want to it.
krileon
