For AEPs rarer than the 1 in 2,000, you can edit the temporal patterns file like you have suggested but RORB will not sample specific temporal patterns for different AEPs unless you set up the file as the same format as point temporal patterns. The point temporal patterns from the data hub are separated into frequent, intermediate and rare categories for AEPs. If in the file you were to put ‘very rare’ for the AEP then RORB would use these temporal patterns for events rarer than and including the 1 in 100. If you would like to control which temporal patterns are used for specific AEPs then you would need to set up separate temporal pattern files and multiple simulations.
As for what temporal patterns to adopt, the GSAM/GSDM are options you can use but you would need to decide whether they are acceptable for your catchment.