When using limnono trainer and going into tendencies there are 4 boxes. The problem is that the 3rd box which is the birth year from what I've worked out is the only box that can be edited independently. 2 of the other boxes are the current year and also the face and another box which I imagine is player portrait. The problem is that all 3 of the remaining boxes have to have the same value as the 3rd box which means when you edit the current year you will change the age the player has or if you try change the age they will no longer have the correct face. This means you can have the correct face or an age of -1562 or something like that.
I know it's early days for modders, but I can only hope it gets fixed as even the translation of limnono trainer is dodgy althought appreciated. Nonetheless in the attributes some of the attributes oyu can edit don't even exist in the game and some are in the wrong order so you can't even use it to create players and have to use the actual in game editor.