Hi Tennet, you should load the file created when you saved your layout.

Usually, custom layouts are stored in Temp Folder in AppData\Roaming\MAXON\YourVersion\library\layout
You can retrieve AppData\Roaming\MAXON\YourVersion\library\ with

c4d.storage.GeGetC4DPath(c4d.C4D_PATH_LIBRARY_USER)

Regarding your second question CallCommand, as the function sound, call a command.
56000 is the ID of the command to switch the layout and 112 is the actual Layout ID but there is no way for 3rd party developer to know him, the way to go is really to directly load your layout file.

Hope it's helpful, if you have any questions please let me know
Cheers
Maxime