To append data to an existing CAS table you can use a DATA Step together with the APPEND=YES data set option.
Please be aware that the table to append, has to have the exact same structure as the existing table, so variable names, types, sequence all have to match. The CAS table is not automatically persisted, so the data is only added to the in memory part.
Essentially it looks like:
data casuser.existing_data(append=yes);
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