Ignoring spring loaded machines that are difficult to control the generaly consensus seems to be the practising on a heavy machine makes using a light machine easier, but is this really the case?

For this I'm going to use an abitrary unit of pressure/velocity called the point.

Lets say you have a heavy action and each increase in volume requires an increase of 10 points, so for a MIDI output of 1 10 points are needed and for 255 2,550 points.
Therefore you learn how to apply pressure in units of 10 +/- 4

Now lets say you want to play on a lighter action that requires only 6 points +/- 2 per discrete volume change.

The person used to the heavy machine is accustomed to less accuracy in the weight applied to each key press than the person used to the light machine, so why would it be easier to change from heavy to light than from light to heavy?

If you're accustomed to a light action, you'll find it hard to press the keys on a heavy one. The feel will seem entirely wrong.

I don't know, though, whether learning on a heavy action translates to skill on a light action.

Anyway, such generalities are moot. Do whatever you like, and the experts be damned.

You'd be surprised that by simply changing the sensitivity of the keyboard the action can seem like a completely different keyboard. Try that ... and forget trying to assign numbers.

If you want to play well on a light action keyboard, practice on a light action keyboard.

If you want to play well on a heavier action keyboard, practice on a heavier action keyboard.

I have a fair amount of technique and sat in with a group that had a keyboard with an unweighted action. I couldn't play it, it was a nightmare. Even after 15 minutes I was not comfortable ... and I impressed no one.

The numbers thing was just to illustrate the point, a comparison might be footballers who will at times practise with a tennis ball - you need greater accuracy with the smaller ball, similarly you need greater accuracy to control a light keyboard.

If I want a really heavy action I just go and find a poorly maintained tracker action organ and pull all the couples out.

Though none are great, not all unweighted actions are equally bad for piano. I think the worst ones suffer from three things that make them nearly impossible to play well. One is that there is often so little difference between the velocity needed for "quiet" and the velocity needed for "loud" that subtle dynamic variants are nearly impossible to control. Another is that the common short pivot points mean that the back of keys play differently from the fronts of the keys (especially evident on black keys). A third is that the lack of resistance and (usually) rounded key edges means that it is quite easy to accidentally trigger the note adjacent to the one you're aiming for on your way to striking a distant target. OTOH, about that last one, I have heard the argument that it is worth sometimes practicing piano on an unweighted board because that demand for greater accuracy prevents you from getting away with things you can get away with on a real piano!

In the acoustic world, within the range of what is considered acceptable norms, it is easier to adjust from a firmer to a lighter touch on short notice. That's about as far as this limited analogy goes. Outside of acceptable ranges, too heavy or too light are actually damaging to technique and make adjusting to normal a slow process.

Using keyboard setting to change the touch works better than it should since the mechanism isn't affected, only the touch response. However, I think it further makes the point that what we prefer becomes what is correct. I find that I use this mostly with the EP's because I often don't like the preset curve. It makes a huge difference on EP's that I previously disliked. I tinker with them and make a variety of changes. For AP's, I like it at normal or one notch heavier.

On any given day, I'll play on 10 different pianos & DP's in our store. I've learned to adjust on the fly, but then I'm playing easy pieces.