The height change will be at a nominal ratio of 3.5:1. Shorter raises, longer lowers. Example: .25" X 3.5=.875" and
.5" x 3.5=1.75"
Due to angles involved the accuracy will vary slightly but should be accurate to a max
of 1/8" error working at 2" change or less. That has been my direct experience.
I wouldn't lower the rear at all due to already limited corner clearance. It can and has been done but it further limits the clearance available and scraping hard parts like the lower fairing and eventually the pipes or centerstand arm, begs to unload the tires and send the bike skating on its side. This is actually the best reason to raise
it, not lower it, for those who ride pretty aggressively. A nice additional benefit is lighter steering due to a reduction in the caster angle at the front end.
This is often done in conjunction with raising the front as much as 1/2" by sliding the fork tubes down through the triple tree clamps.
One consideration is that as you raise it, you effect more lean on the sidestand. It gets pretty extreme after about 1". A spacer can be added to the sidestand foot if needed. Lowering it may require cutting the sidestand length and will make it harder to get on the centerstand. Just things to be aware of.
Here's a link with some pics to a thread started by Bastardchild about his link change. Hope this helps.