The vocabulary list (RIF-CS Controlled Vocabulary) for use in RDA is not closed. Rather, you can choose to use your own types if none of those in the vocabulary fits your data. These are called 'user-defined types' and are accepted by the system without affecting your record.
However, because consistency in types enables some deep search techniques and in some cases, enriched display in Research Data Australia, it is good practice to use the existing types where possible.
If you think your user-defined vocabulary would be useful for others and should be included in the ARDC vocabulary list, please email services@ardc.edu.au. Your suggestion will be considered by the RIF-CS Advisory Board (RAB) as part of the ARDC Change Management process.