You are going to need to remove the upper intake. It's possible to do it without removing it, but it is 10x the pain in the ass to do it that way than to just remove the upper, and most people don't have the correct type of allen wrench to do it the harder way anyway.
Installing the AFPR without a gauge is a terrible idea. You will have no way of verifying your fuel pressure setting, and trying to set it close "by ear" is a total crapshoot.
So long as your stock non-adjustable regulator is working properly right now, do it right....don't do it twice. Wait until you get a gauge before you install the new AFPR.