Andrew and Jeff, thanks for ur answers.
Yes it makes sense.
My scenario is, that about 180 mxd's are produced manually a while ago (and set the scale of all Dataframes to fixed 1:10'000)
Now the map designer came to me, telling me she wants, besides other changes which work just perfeclty, to change the scale to 5'000 in some of the dataframes...
so in my situation it would be sweet to adress the scale via arcpy eventhough its previously set to fixed...
arcobjects - i only know it a tiny bit from java, but could i use python aswell?
greetings
thomas