In your olcSyncrepl directive you can set the search filter for the entries to be replicated. The default filter is
Replace it by
'(&(! (objectClass=class1))(! (objectClass=class2))(! (objectClass=class3))(! (objectClass=class4)))'
Or add this to whatever filter you have (hope I got the paranthesis right).
Sorry, I misclicked for the reply and didn't send it to the list. And what I said prevents all entries using any of the four classes from being replicated and concerns the olcSyncrepl statement of your actual data. The exattrs is no longer needed if you use this filter - and you might want to let it out, if any of your four classes' attributes are used by some other class.
But I wonder if I didn't misunderstand your question. The values of objectClass are not in your data, they belong to the schema, cn=schema,cn=config. Do you replicate your cn=config and want to have a different schema on your consumer with respect to the provider ?