It is not possible to set in xWMS configuration file that some layers are not shown by default. Now it appears that it attaches all listed layers from WMS at once. For example if there are multiple orthophotos of same area but with different dates then it would be more easier to switch layers than to attach multiple xWMS files for each layer. Tried to delete layers from key or key but result is not as expected.
There is already a change request from year 2010 but most likely lost - CR (#306124).
Development have reviewed Bug 1056064 and it has been closed with 'No Action' given WMS layers were recently removed.
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Bentley is actively making working with background data worse.
And WMS 1.3.0. still doesn't work for XY interchanged SRS so no layer editing possible.
There is now backwards improvement that Layers are no longer available at all.
Now have to use Utilities menu in Raster Manager to modify the WMS by adding and removing the Map layers you want to display.
So instead of two clicks we have to mess xWMS configuration which means manual edits to xWMS are lost after each edit. This is wrong move, we need layers but with slightly updated xWMS format so it allows to disable some by default.