Deleting attributes of a Inactive Planning level

Hi experts,

I'm facing troubles, trying to delete attributes of a planning level on the Response planning area (actually is the standard planning level "PER").

I added all available (standard) attributes), in addition to "771-Opearational/Tactical Planni (5)" at the planning level "PER", and I saved changed.
I changed my mind, considering I made mistakes doing this.
I tried to delete those attributes marking "Mark as deletion" flag, but this is no possible (flag is blocked).
I tried to reactive the PA, but this is no possible because now there is an error due to my change on "PER" planning level.
It's even no possible to delete completely the planning level in object "PER" , because two Key figures are related to it (PERIODID and HKFPER).

So, what should I do now?
Do I have to redo all, starting from deleting KFs, then the planning level and at the end recreating all?
Thank in advance for your support.
Best regards,

Luca