changing a DVD tag using Apple
1.  create a .dmg file (disk image)

load the DVD, DVD player will engage. click - DVD PLAYER > Quit DVD player.

click - Applications > utilities > Disk Utilitiy.app

in Disk Utility, highlight the DVD in the disk drive.  click - File > New > 
Disk Image from (name of disk)

a 'Convert Image' box will pop up: you can name the file and select the 
location where the Disk Image is will be saved.  

click - Save.
 
2.  create a Quicktime file

first you need a high-quality converter.  I use MPEG Streamclip 1.7  It can be 
downloaded for free from http://www.squared5.com/   Do that now.

Next, go to where you have saved the .dmg file.  Open it.  You may have to test, 
but usually it is the last VOB file (video object) Select the correct VOB file, 
load it into the video converter (drag, drop)

in Mpeg Streamclip, click - file > convert to Quicktime - 
'MPEG Streamclip-Movie Exporter' box will pop up in 'Compression:' window 
select  > Apple DV/DVCPRO-NTSC  in 'Quality:' slider select 100%> in 'Frame 
Size:' select 720x480 DV-NTSC   in 'Options...' > 'Aspect Ratio:' select 16:9   
'Frame Rate:' 30

click - 'Make Movie' 

a 'Create New MOV file' box will pop up.  Name file in 'Save As:' select 
location in 'Where:'

click - 'Save'

3.  create new Digital Video with new tag

load Quicktime (.mov) file into video editing program.  I use FCP but there is
no reason you can't use iMovie

locate edit point where embedded tag begins and cut the video, replace with 
new tag

share/export

4.  create new DVD with new tag