In the tdf file. You have to edit the tdf file manually.
Reaction=tiresmoke Tex=smokewhite.tga Max=1024 Scale=(1.0,1.0,1.0) Growth=(4.0,3.0,2.0) ASDEnvelope=(2.0,0.2,3.5) DestBlend=InvSrcAlpha SrcBlend=SrcAlpha
Reaction=dust Tex=Dustroad.tga Max=128 TopSpeed=104.0 Scale=(1.0,1.0,1.0) Growth=(4.0,3.0,2.0) ASDEnvelope=(2.0,0.2,3.5) DestBlend=InvSrcAlpha SrcBlend=SrcAlpha