Did you make the change to go via MUC or not? It is a bit unclear
The regulation is pretty simple in that if a passenger is downgraded on a flight where the regulation is applicable then 75% of the fare is due to be reimbursed to the passenger
It also seems that EK will not pay up without a fight
Unfortunately the one person I have seen who has posted having tried to take it to court seems to have failed after failing to turn up to present their claim ; apparantly EK sent no one from its side to defend it
The more recent poster ( in this thread ) never did come back with information on the outcome of his claim
Unfortunately for you in your specific case , the flight which has been downgraded ( DXB-ATH on Emirates ) is not one which is covered by the regulation , so you would have no claim in this case
If it was an ATH-DXB sector, then that would be covered
In order for a flight to be one under which EC261 applies , in simple terms has to either be
A flight departing from an airport in Europe - on any airline
or
A flight departing from an airport outside Europe to Europe - on a European airline
( it is slightly more complicated than that but is close enough for most purposes
)