You can choose wireless channel/bandwidth only in AP& AP router mode.
In other modes including AP client router, its channel/bandwidth must follow root AP, no way to change it manually.

In Bridge with AP mode, do not follow root AP's channel/bandwidth and mode. So we should choose in Client Router Mode. :D:D:D

If you set a different channel/channel width as root AP, the connection between your root AP and your WA7210N will down, you can have a try on this.
I guess the the channel/channel width option on WA7210N's bridge with AP mode is only used when you want to manually type in the root AP's SSID/MAC without 'survey button, because at this time you need to select a same channel/channel width along with the SSID which you want to connect to...
So it's meaningless to change them if you use 'survey' option.

It's similar in AP client router mode, you don't need to change these settings for your local wireless AP.
There is only one radio in WA7210N, it can only works in one channel at a same time. In AP client router and bridge with AP mode, WA7210N need to communicate with both root AP before and clients behind at a same time, so it's local AP's channel/channel width must follow root AP.