I have a new T-80 box so that I update my T-30. My question is can I use the old config file from my T-30 for my T-80.
the firmware version on my T-30 is 188.8.131.5240389
You can move your configuration. See:
(Move a Configuration to a New Firebox)https://www.watchguard.com/help/docs/help-center/en-US/Content/en-US/Fireware/basicadmin/config_file_use_new_model_wsm.html
If you have time, I would suggest using this as an opportunity to audit whatever policies you have to determine if they're still needed/valid.
WatchGuard Customer Support