If your caste and income certificate for KCET application is still under process and you have been provided an RD number, you can use the RD number as a temporary reference while filling out the application. The Karnataka Examination Authority (KEA) often allows candidates to provide the RD number in such situations, as it shows that the certificate process has been initiated. However, ensure that the certificate is issued and available before the document verification process, as it is mandatory to submit the actual certificate at that stage. Keep track of the issuance process to avoid any delays. If you're unsure, contact the KEA helpline or officials for clarification and ensure compliance with their guidelines.