You can draw your 2D drawings on different layers in GDL object '2D symbol' section. Or draw it first on the floor plan and paste into 2D symbol. Please note, that it does not support polylines. All polylines needs to be previously converted into lines and circles.
2D symbol has layers (like in ArchiCAD) but only with numbers - from 1 to 16.
Visibility of these layers can be controlled in 2D script via command:
Where fragment_index is number of layer and use_current_attributes_flag can be 0 or 1.
0 shows pens, line types and fills how it been drawn
1 replace these attributes with defined in the script (i.e. PEN number, LINE_TYPE number, FILL number)
You also need to create a parameter, let call it symbolProjection. Set it to number.
In parameter script use