Thats a good point indeed, but SetParameterAsText and SetParameter seems to be void functions?
The parameter 31, 32 and 33 are defined as layer files. I assign a shapefile with walls to 31 and a shapefile with buildings to 32 and 33 which are then symbolized differently. You are probably right - something is being overwritten, but how can I change these attributes right after the SetParameter command? The walls are added correctly to the map.
if addWalls:
arcpy.SetParameterAsText(31, walls_Shapefile_result)
arcpy.SetParameterSymbology(31, lyr_walls)
if bVulnerability:
if addRiskAngle:
arcpy.SetParameterAsText(32, buildings_Shapefile_result)
arcpy.SetParameterSymbology(32, lyr_building_risk_a)
if addRiskSettl:
arcpy.SetParameterAsText(33, buildings_Shapefile_result)
arcpy.SetParameterSymbology(33, lyr_building_risk_sv)
Here, "building_shapefile_result" is simply a string containing the path and the name (with extension) of the shapefile. Below is a snapshot of the parameter table in the tool.