That’s not an option 
To be more precise on why I hope this fixes my problem: I have a Contact item that I persist in database. I want to count how often this Item changed its state. @rlkoshak suggested (Count number of times a door got opened) to use persistence sumSince() function to do that, but that doesn’t work as @rossko57 explained: Persistence sumSince() doesn't output a valid numer, only zero because a Contact is represented by a string, that can’t be summed.
So if I use the persistence data of the Contact (which gets persisted as 0 and 1) I could take that data, interpret it e.g. as Number and then do a sumSince().