You're going to make me pull out the old physics lesson aren't you...
This is something many people don't understand at first, but the only way to stiffen a spring is to adjust it's coil properties... that would require a new spring to be swapped out.
By screwing or unscrewing the adjuster, you would only be raising or lowering your vehicle. Some people "say" they feel a stiffer ride due to a lift. This is physically impossible from a spacer lift... what they are feeling is a physical phenomenon with the suspension geometry, where the body rolls less with the lifted geometry due to a higher virtual roll center. The other element to feeling a stiffer ride is upgraded shocks, but they don't provide extra support for a heavy front end.
The misconception comes when people feel like they are compressing the spring more to fit the extra spacer in. Yes, the spring is compressed more in the unweighted strut... but as soon as you add weight, the spring will be exactly the same height.
Here's an old picture I used to explain how the BDS didn't affect the spring's compressed height when under weight.
Spring rate for these springs is linear. The unit for the spring constant is force/displacement. So displace it 1 inch, and it produces, say, 300 lbs of force; displace it 2 inches, and it will produce 600 lbs of force. However, in a vehicle situation, it's almost working in reverse because the vehicle and spring are at equilibrium. Vehicle's weight = force on spring. So if you work backwards, you can determine how far the spring will displace when under said vehicle's weight.
If you want a stiffer ride to compensate for a heavier bumper, see the factory springs thread:
viewtopic.php?f=15&t=158 For now its the only way to get a stiffer spring/ride.
Although, your idea could theoretically produce lift if adapted properly. It would just be adjustable lift. A similar thing is possible if you just chuck your shock in a lathe and cut another clip recess into the housing for the lower spring perch.
Here's to thinking!