cartiage for Kenwood L07D genuine tone arm

With all due respect to Johnny, and as Dave partly indicated, Johnny's response to the question about effective mass is incorrect on all counts. The effective mass is a function of the distribution of the mass of the tonearm from pivot to headshell, including the cartridge mass, (not just the total mass per se), which is why you cannot determine effective mass by simply weighing the tonearm, and the counter-weight also contributes to effective mass by a factor related to the square of the distance from the pivot point to the center of mass of the CW times the mass of the CW. Thus, the "subweight" increases effective mass on both counts; it shifts the center of mass of the total CW further away from the pivot and it adds to total mass. Apologies to Johnny...

Since the effective tone arm mass is not simple measurement
If I change a aftermarket headshell, how it will change? Can I ausume it add or decrease the difference only?

Jagdzaku,
To answer your question, almost. With mass behind the position of the cartridge, 100% of the weight difference does not subtract or add to eff mass. This is a trivial amount. The stock shell looks to be of very high quality, but it might be interesting to experiment.

To clear up some misconceptions, if you increase the weight of the counterweight and bring it closer to the pivot, eff mass will decrease with the change of distance.

I think too much emphasis is placed on resultant resonant frequency. IMO you'd be better off asking users which carts are a good match, which combination seems like it's made in heaven. Some carts seem to sound better with mass that puts them a little out of the recommended resonance range. While you don't want that undamped resonance approaching the audio band or excited by a warp, best results are not defined by "perfect" 10Hz resonance.
Regards,

"To clear up some misconceptions, if you increase the weight of the counterweight and bring it closer to the pivot, eff mass will decrease with the change of distance."
That's only because eff mass will vary as the SQUARE of the distance between pivot and CW center of mass, whereas the relationship between eff mass and CW mass is first order. I'm writing this, because I don't know where there was a misconception. One interesting thing that falls out of the equation is that if you use a relatively low mass CW, you can have more control of eff mass simply by sliding the CW toward or away from the pivot vs using a "heavy" CW. I think this is what Technics (and other makers of vintage Japanese tonearms) had in mind with their design of the EPA100, which they claimed could be used with cartridges that vary widely in compliance. Modern tonearms have tended to go in the other direction, with heavy as possible CWs mounted close as possible to the pivot, to reduce inertia, I think. My Triplanar came with a variety of interchangeable CWs, so the CW can always be close to the pivot. But look at the very expensive Durand Telos tonearm; it has a rather long rear projection and a relatively light CW compared to some others and even to the Talea.