I have seen a lot of modifed cabinets. The thing about them is that people who know their stuff can spot them instantly, and usually laugh at them, or post pictures of them on the internet and invite other people to laugh at them. (That goes for oversize panels on old school 19" cabinets too).
That cabinet in the picture is what I believe is called a lowboy cabinet.
Basically what I am saying is that it may not turn out as well as you would think, and it certainly wouldn't cut too much weight from the cab, as that top section really isn't all that heavy. And you end up ruining a cabinet that you may not own for the rest of your life. I modified (ruined) a Pac cabinet once, and I had to trash it once I didn't want it anymore because nobody wanted it.
Your time might be better spent repainting and refinishing what you do have instead.