Everything?? Even O/S data?
What I would do is create a different management class in the same domain for 2555 days, then, find out the exact data they want to keep for that long and use include statements to direct the data to the correct management class. For instance, have the default retention set to the 33 days for, say, the o/s stuff and create a new management class 7_YEARS (with retention of 2555), but then have an include statement like:
include C:\mycriticaldir\* 7_YEARS
Since it is simple to install an o/s and configure TSM, you end up saving $$ in media, yet you meet the requirement (sometimes government mandated) of storing that particular data for 7 years.
If it is just a few servers and for a certain period of time, I would just set up an archive copygroup with a 7yr retention, archiving the select data through a schedule that you can run a couple of times - or annually if that is the need, and use "-archmc=7_YEARS" in the schedule if the default management class isn't 7 years.
I would only do this if this is something you don't need everyday as archiving tends to drive up the tsm database usage, and if there are tons of files, and the schedule is running daily you will have a whole new set of problems.