Can I modify the band that comes with the Apple Watch

If you buy retail online with Apple, you can mix and match the watch and the watch band that you like.

M1 Mac mini, macOS 14.1.2;  Watch, series 7 GPS/cellular, watchOS 10.1.1; iPad Pro 2nd Gen, iPadOS 17.1.2; iPhone 12 Pro, iOS 17.1.2; TV 4th Gen, tvOS 17; HomePods, audioOS 17.1.1 and Airport Express w/ Airplay 2

you can use any band you wish

Buy Apple Watch Bands - Apple

the big model share bands across the board and the small version too

See compatibility details 

Click the Watch link at the top of this page to learn about the Series 9 and the watch bands that you can choose to go with it.

You don't have to settle for a default watchband.