When you replace a transmission on a 98?

Honda accord automatic is it a good thing to replace the flexplate and flywheel at the same time?

The flexplate and flywheel are the same part. The flexplate is found on an automatic and a flywheel is on a manual car. If you meant to say torque converter then I would suggest it be replaced at the same time as the trans.

Flexplate is essentially the same as a flywheel. Flywheels are used with a manual transmission while flexplates are used for automatics.

Automatic it is not required to resurface or replace the flex plate because it bolts to the toque converter unless it is damaged but hey you want to spend money that is burning a hole in your pocket by all means it's your car

You have one or the other. A "Flexplate" is a flywheel for automatics. Seldom does a flexplate go sour, but a flywheel can have some were & tear groves in it, or warped.