For a short 4 week run I might consider keeping the assistance work pretty low. It looks like you have a fairly intense program there, with a regular maxing out. I'm inclined to say just follow the program for the four weeks and see what happens before tinkering with it.
If you are really working hard, that looks like a strong program.
Or, if you want to play with GHR, for example, maybe sub them for the back ext rather than adding them in as another element.
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