I'm doing this as an example of what a Mod should be.
A good example is the iOS theme. It only updates the necessary parts of the rom that need changing to get the desired effect. EDIT JAMEZELLE: also makes debugging easier
So making an update "mod"
I'll upload a shell update and explain the update script.
Unzip the example.
Inside you will see 3 folders. system data META-INF
system is where you are going to put your extra apps/ringtones/bootanimations
if you want to add an app open up system and make an app directory and drop in your app(s)
if you want to add ringtones from another rom open up system and make a directory called media and drop in the audio directory from the other rom
if you want to add a different bootanimation the open up system and make a directory called media and drop in the bootanimation.zip from another rom or theme.
data is where you want to copy downloaded apps that you don't want on system
if you want to make an add on pack this is prob the best place for extra apps like wireless tether etc...
open data and make a directory called app. drop your apps there.
this holds the update-binary and update-script as well as other information needed if your recovery requires zips to be signed. (not necessary on droid 1 using clockwork recovery)
the update script is the only thing you want to modify. it is located at:
navigate there and open the update script in a Coding text editor such as gedit or nano in linux or notepad ++ in windows.
It should look something like the following:
This update will copy whatever is in system and data to the rom.
mount("MTD", "userdata", "/data");
mount("MTD", "system", "/system");
set_perm(0, 0, 0755, 0644, "/system/app/foo.apk");
set_perm(0, 0, 0755, 0644, "/system/app/foobar.apk");
The set_perm part sets correct permissions for any app copied over. Change it accordingly.
After your done rezip the system data and META-INF directories into a new zip and flash away.
If successful upload your results and share it with everyone else.