Yes. You can edit the file; just keep the same format as what's already in there.
For example, this comes from my backup of an early version of the AD software:
---------------------------------------------
Available hard disk images:
---------------------------------------------
0001) HDSK01.DSK: Altair Hard Disk BASIC
0010) HDSK02.DSK: Altair Accounting System
0011) HDSK03.DSK: Mike Douglas' 88-HDSK CP/M
---------------------------------------------
If I was to add another hard drive image, I would add a new line, like this:
---------------------------------------------
Available hard disk images:
---------------------------------------------
0001) HDSK01.DSK: Altair Hard Disk BASIC
0010) HDSK02.DSK: Altair Accounting System
0011) HDSK03.DSK: Mike Douglas' 88-HDSK CP/M
0100) HDSK04.DSK: Tom's Programs
---------------------------------------------
This should work fine with the disk selection command in the main menu.