There are some customs here and there which have "zero" difficulty for pro keys, where really that isn't the case
I opened up the metadata file (I am on PS3 so I have only a single songs.dta file for all customs) and in fact those songs show real_keys = 1.
I just want to put some more reasonable difficult value there, and it seems all that's needed is just change the value in the metadata file. Piece of cake really...
Now, my question is actually: what are the numerical values that correspond to different difficulties in the 0-5+ scale used by the game?
It should be very simple to know (I could in fact just try out different numerical values, and check how they are displayed in-game), but I was a bit surprised that I wasn't able to find this simple information in the authoring documentation... or did I simply overlook it?
Also, generally speaking, I can see that authors have assigned all kinds of numerical values with a level of precisions, so you could have instruments with a single-digit difference, but they show up with the same difficulty in the 0-5+ scale. Do we have any sort of guidelines or criteria for properly assigning an instrument's difficulty score, or is it totally up in the air at the author's mercy?