I thought of that It was the only things I could disable, because there is nothing to be found for "frank*"
Great Tip, that helped - thanks
I did not edit the PLC File(s), but one of their Names "GES_POI_PLC_OBX" brought my Attention to various Library Files. I've edited them with MCX, deleted every Building/Object for Frankfurt. Now the Skyline is clean without any double or "orange" Buildings. For other Users, the Files are:
GES_POI_Library01.BGL
GES_POI_Library02.BGL
FTX_GES_Library_LS.BGL
All located in ...\EU Germany South\Orbx\FTX_EU\FTX_EU_GES_05_SCENERY\scenery
For the Objects/Buildings: everything except "Maintower" is prefixed with frankfurt.