Re: microtonal music on a 'standard' gtr- yes possible but with severe limitations.

You can indeed produce microtonal intervals on a guitar without removing or repositioning the frets.
As with any stringed instrument you can adjust the open string tensions to whatever you may choose (within mechanical limits)
The difficulty with this approach is that if you still have the original frets in position, and have not changed the bridge to nut difference, intervals that you play on any one string using the frets will result in 12edo intervals.

If you want to make your fretted instruments more universally microtonal, this webpage will help you.

http://www.lucytune.com/guitars_and_frets/frets.html

On the following webpage you will find a few of the thousands of possible alternative open tunings for guitar and bass.
These alternative open tunings will work satisfactorily for all 12edo and LucyTuned guitars.

http://www.lucytune.com/guitars_and_frets/guitar_tunings.html

If you wish to experiment further with guitar tuning and fingering games, you might explore capos, both full, and partial.
I have even tried using two or more partial capos simultaneously to produce more open-tuned possibilities.
Some of these alternative tunings also work very well for tapping, and with violin/cellos bows and ebows.

Charles Lucy - lucy@lucytune.com ------------ Promoting global harmony through LucyTuning ------- for information on LucyTuning go to:
http://www.lucytune.com
for LucyTuned Lullabies, go to
http://www.lullabies.co.uk
Buy CD from:
http://www.cdbaby.com/cd/lucytuned2

Download via iTunes:
LucyTuned Lullabies (from around the world) Original
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewAlbum?playListId=5165249

LucyTuned Lullabies (from around the world) II
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewAlbum?playListId=75504906