To answer your questions:
How do I create these entries?
Open profile.ini in Notepad, preferably when SeaMonkey is closed.
1) Can I rename these profiles (assuming I change profiles.ini to match) so I know which is which?
Yes
2) Is there a way to merge profiles, or to transfer mails and contacts between them?
I don't know of any way to do this automatically.
mails: copy the file and paste into the preferred location. Make sure it has a different name than any other of your files.
I don't use contact lists, so I can't say exactly how you would move them.
The next profile in the list would be:
[Profile1]
0,1,2,3 to n n being the last number.
Name=
whatever name you decide to call your profile.
IsRelative=
1 or 0
1 I think is the standard location, ie drive C. You just need Path=Profiles/xxxxxxxx.Default User (or other user name)
0 I think is if you have your profile in another location, I have my profiles on Drive J. So I use IsRelative=0
Path=J:\Mozilla\SeaMonkey\profiles\xxxxxxxx.Web one
