When taking part in a CSA the Commission us to change our indirect cost method to 20% although only a max. of 7% will be reimbursed. Is it possible to change it back to 60% for our RTD projects?

One of the criteria for using the derogation model is that it is only available for specific funding schemes. This does not include CSAs. Therefore, in your case, you should change the indirect cost method to 20% although only a max. of 7% will be reimbursed. Your organisation can then change it back to 60% for RTD projects.