I see no method defined in the installation manual. It appears to be programmed at the factory with no way for the end user to inspect what was programmed.
Who provided the ELT? If provided by CubCrafters I suggest you ask kit support what configuration they order.
"G. ELT Programming NOTE: Programming is performed by customer if so equipped or through a programming sheet supplied to ACR Electronics, Inc. with an ELT order. For information on ELT programmers and training, please contact ACR Electronics, Inc."
H. RS-232 Acceptable Nav Data
1) NMEA 0183 baud rate is 4800.
2) Aviation protocol baud rate is 9600.
3) Programing of the ELT 345 will determine the input of 4800 baud NMEA navigation data or 9600 baud Aviation protocol navigation data.
4) The ELT 345 will parse GGA, GLL and RMC simultaneously. Output configurations that write GGA, GLL or RMC sentences at 4800 baud as specified in NMEA 0183 will be suitable.
5) GPGGA is recommended if available.
What GDU 465 output data formats have you attempted?