Say the blade is 95g mass and the weight distribution is 60/40 front rear.
57g/38g front rear
You add 5g to the rear, let's assume it's to the very rear for simplicity sake.
57g/43g front rear.
43 divided by 100 is 0.43. Your front/rear weight distribution is now 57/43, and your total mass is 100g.
You added 5g to 95, so:
5 divided by 95 is 0.0526 ~
You added about 5.3% more mass, and you gained 3% rear weight distribution. However in reality you will gain less, perhaps more so around 2.3% or so.
Your blade is now heavier, but the rear has more mass and thus more weight when the blade is placed horizontally. The total mass of the blade is now for simplicity sake part of the swing, BUT your head weighs less and is easier to move around.
EDIT: Now I understood what your question was.
If you magically merged the weight in, and the blades were absolutely identical, I guess yeah.
I can imagine that having a purpose-built heavy blade could theoretically perform better than an "identical" homebrew blade with the same mass and weight distribution.
The wood would need to be thicker for one, if it's the same material. Actually it seems very hard to produce a handle-heavy blade that's the same composition as it's head-heavy cousin, without some kind of modifications, if you're gonna keep the middle ply the same thickness. Mass would need to be added into the handle, but if the handle is solid already, it'd complicate things.
Rather than worry about things like this, why not just slap some mass onto the handle with grip tape and nails and try it out? Blade engineering is ****ing difficult.
EDIT 2: You know, adding nails and whatnot into the handle could even potentially increase or maybe even decrease the blade's speed, but that's really pushing it I think. I wonder if anyone's ever made any impact tests on blades with wood handles vs steel handles, for example. I'm thinking that the handle won't really affect the blade face so much, but they ARE kind of binded together so very impractical, drastic changes to the handle might produce a change to the complete package, so to say.