Grab the Cheat Engine trainer here that I maintain, I updated the slot cheat to work with the new DLC slots, dice chests and so on. goo.gl/JjVpC
Did some testing on this one as well.
Haven't gone to any of the DLC slots yet so just tried the normal Sanctuary ones.
Slot locking seemed to work though i'm not entirely sure how to modify the setting to force any of the other prize rewards besides the legendary weapon since there seems to be no documentation.
There also seems to be some sort of conflict with the update/modify level setting and the slot lock as having those two active resulted in a fatal error and the game crashing when I moused over to look at the item that the slot machine popped out.
Additionally, if I enable update item level (mouse activated) that seems to be active for the rest of the game session and there seems to be no way to actually deactivate this. I tried unchecking the script itself, I tried unchecking the whole script category, I tried unchecking Enable to disable the entire trainer, and I even tried closing the trainer but the script remained active which is interesting. It is probably this issue that caused the fatal error since this probably resulted in a conflict with previously activating change item level (F2 activated) since the trainer states that you should only activate only one but since the mouse activated one has no way to actually turn off, they end up conflicting.