Overwrite propertyset value with dynamo


I was wondering how I can overwrite a value with the use of dynamo. With the program that I made I get the following error: “Property.SetValue operation failed. eWasNotOpenForWrite”. If I’m right this means that this property value is secured which means it cannot be overwritten, but how can I change this status?
My dynamo scheme:

my created propertyset, with included property:

the “default” value of this property should be overwritten by the value of the list as seen in the first images.

Thanks in advance.

okay, so I tried some things and it seems to be working now. But idk what I changed. Once I figured it out I will update it here.