You might want to peruse this thread:
It's pretty extensive, even on the first couple of pages.
Someone who's done more modding than me can likely bring more info. I'm working on the premise that, with it being more head light, it's easier to generate racquet head speed, as well as being more joint friendly, and easier to swing over a long match or hitting session. So all things being equal, I think the power should remain more or less constant, compared to a lighter, HH, stock racquet. If you lose some power, add a bit of lead tape either at 3 / 9, 10 / 2, or 12.
If you're unsure if you're going to like the mods you're about to do, I'd choose one that's easily undone. I used DAP Blue Stick in the handle, rolled into long thin strips, and wrapped them in cling wrap. That way, I can easily remove them, or add to them, as needed. Silicone can be removed, but it's a bit more of a pain...but I'll likely replace the Blue Stick with silicone on the wife's racquet when she knows she's set on the mods.
Also note, a big part of the whole Graphene thing, per the marketing propaganda, is that it makes the racquets more polarized, taking weight out of the middle. My wife and I tend to like more depolarized racquets, generally speaking, so adding a bunch of weight to the handle un-does its design intent. That being said, the Graphene Instinct Rev felt pretty good in stock form...but it feels even better now, with the extra weight and more HL, at least to us.
As always, YMMV.