Be careful not to tinker with the 5x5 template too much. If you were to take the recipe for apple pie & use pears instead, it obviously wouldn't be an apple pie, if you know what I mean.
I wasn't aware that cable cross overs was in the template. Well done on wanting to do the decline presses, they're great.
The concept of 5x5 is a pretty basic one, progressive overload. If in one week you increase your squat, deadlift & bench press...you may not be able to put in 101%. Don't think about it too much, just get in there & create a PB on one lift a week