Group policy - drawing extension

We use to attach dxf files to part files (copy - paste as references). DXF files are used for making programs for punching machine. In this case dxf files are listed in BOM. I don't want that dxf files to be listed in BOM. I try to set in GP drawing extensions but no change even I added dxf extension to list.

Is there any other method to accomplish that?

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