in our custom schema we have used several attributes with the syntax:
attributetype ( myAttributeType:106 NAME ( 'casFileContent' )
        DESC 'Contains the file'
        SINGLE-VALUE )

We defined this schema before this syntax was dropped.

Everything worked for a long time. Now with OpenLDAP Version 2.4.39 and newer a slapcat does  no longer export this attributes as MimeContent, but as plain text. So the ldif can't be used for importing. So I started a research why and found that this syntax was dropped. But for downward compatibility shouldn't it still export this syntax as mime content, shouldt it?
This would be important, since in inetorgperson.schema the 2 attributes userSMIMECertificate and userPKCS12 still use it.

What syntax should I use for files stored in LDAP?
And even more important, how can I change the syntax of a attribute. Is there a migration strategy to change the syntax of a attribute?