Hello,
Yes, if you extend your Active Directory schema with new attributes, they will be available in Adaxes same as other AD attributes. You can proceed with adding new attributes and use them instead of the custom attributes that are available only in Adaxes. Just make sure that LDAP names of the new attributes do not match the LDAP names of Adaxes custom attributes (e.g. adm-CustomAttributeText1, adm-CustomAttributeBoolean1, etc.).