Is there any way to auto comment scheduled archives based on a .txt file?

Its sounds like you might be a bit of a programmer.
based on what you want to do tats a good thing.

There may be other ways but this is the first thing that came to mind.
It should work. you will have to write a few lines of code to automate this task but a fairly simple .vbs script should do the trick let goolge be your friend if needed.

step 1) create a backup task that does what you want
hard code some unique constant as a description such as "mytemplate123"
do NOT put this job on the acronis schedule.
for what you need to do the backup job will not need to contain any pre/post tasks.

step 2) search folder
C:\Documents and Settings\All Users\Application Data\Acronis\TrueImageHome\Scripts\
for your unique constant
you will find a ".tis" filename that contains the string.
in fact the exact string will be
description="mytemplate123"

step 3) lets assume you want the comment text to be these 5 lines...
SPECIAL TASK
THIS IS LINE 2
THIS IS LINE 3
THIS LINE CONTAINS QUOTES "HELLO WORLD" HOW ARE YA
THIS THIS IS LINE 5

to get a new line its string

to get a quote its string "

so what you need to do is to write a batch job that takes your file
search for string description="mytemplate123"
and replaces it with string
description="SPECIAL TASK
THIS IS LINE 2
THIS IS LINE 3
THIS LINE CONTAINS QUOTES "HELLO WORLD" HOW ARE YA
THIS IS LINE 5"

step 4) you now have built a ".tis" file that when run will create your backup and the .tib files will contain your desired 5 line comment.
to run this ".tis" file you pass it as a param to "homeservice.exe"
"C:\Program Files\Common Files\Acronis\TrueImageHome\TrueImageHomeService.exe" /script:"C:\Documents and Settings\All Users\Application Data\Acronis\TrueImageHome\Scripts\4F3D4936-C14B-47C2-95A8-D18E649D0FAD.tib.tis"

step 5) when acronis successfully runs the backup, the '.tis' file will change
with additional detail about the sucessful run.
what you need to do now is to replace the customized description with
the original unique tag thus restoring the ".tis" file back to a state such that
the next run can repeat the above process for that ".tis" file.
search for string
description="SPECIAL TASK
THIS IS LINE 2
THIS IS LINE 3
THIS LINE CONTAINS QUOTES "HELLO WORLD" HOW ARE YA
THIS IS LINE 5"
and replaces it with string
description="mytemplate123"

Thanks oracledba.

I can see how your suggestion would work, however, I was hoping to use the True Image scheduler so I could have it auto delete older archives after x amount of full backups. My plan was to have a fairly complicated backup schedule, with 4 or so schedules for different drives/partitions. Not sure I want to try to write something outside True Image to manage all that...

I am, however, curious if I could modify this tib.tis by executing a .bat or script as a post command in a schedule task. There may be 2 problems with this, however... 1) the file may be locked by True Image, and even if it's not, I would have to figure out which .tib.tis file the scheduler is using to update it on the fly...

I will give it some more thought. If you think of something I am not considering, please let me know as well. Thanks again for the info.

If anyone else has some ideas, please let me know.