There are a few companies around that do 'tune' Haldex devices, however you will likely pay quite a bit.
It's not a case of you taking your car somewhere and asking for them to adjust settings and then you leave, you would need to have a new controller installed that allows manual control of things like drive bias in the first place. I haven't heard of any GenV Haldex modifications as of yet as the unit is still relatively new to the platform and is vastly different mechanically to previous versions.
A company called HPA Motorsports sorted out my cousins R32 Golf in the US several years ago with a race controller. Have just looked and they don't appear to have anything available for GenV Haldex units as of yet. No idea if they plan on developing or not. They do have a lot of kit available for the 2.0 Turbo platform though, although it is US spec equipment.
Realistically,you won't get more than 50% front/rear split,(except under situations where the front is slipping a LOT,to satisfy those who bring this up every time Haldex is mentioned....)due to the way the system is configured,and the so-called "race" controllers for previous versions do make an appreciable difference to the speed at which torque is transmitted to the rear,but IMHO they really aren't giant killers.
On average,you're looking at around £800 for older spec cars,and that money can easily be put to an LSD for the front diff,which really does make a difference to traction.
Yes,I do have a Haldex controller on my 8P,as well as a Quaife diff,and I can tell you which makes the biggest difference.
I think for you guys with the 8V,it's going to be a case of waiting for the tuning industry to catch up again,and produce the parts.
Also...there are a number of threads on other forums talking about the relative speeds at which Gen 4 and Gen 5 systems engage,and the economies involved.
As Alex has said above, due to the mechanical limitations of Haldex, you cannot ever get more than a 50:50 split of drive front:rear. You will never be able to make the rear wheels rotate faster than the fronts when Haldex is engaged.
In some limited circumstances (front wheels up in the air, or front wheels on ice) - you can get near 100% torque transfer to the rear axle, but this is more Haldex marketing than real world.
If you have a lot of lock on, and boot it out of a slippery junction, you can get power oversteer, same in the snow. But not on the move with high friction surfaces.
And then, even when you do get the torque transfer to the rear wheels, one spinning rear wheel will render the system useless (the new Focus RS uses a new GKN driveline system to get around this problem).
A limited slip diff in the front (like the AMG A45) is a far better solution to handling and traction, rather than chasing a quicker lock up time on the Haldex controller.
There are a few flat-earthers around who insist that Haldex is every bit as good as Torsen (proper quattro) but quite simply, Haldex is a compromised solution to enable transverse engine cars to have a form of (part time) AWD.