You would have to archive and install the system, however archive and installs and pro apps like FCP, or Adobe software do not always play nice together. Those pro apps put some components into the OS and when you archive and install you loose those components.
So if you have pro apps then it is probably best to just wipe it and start over.
Why do you want to go back to 10.5.5?
You do know that 10.5.7 is out right? I there are no problems that I have seen with it.
There are no "technical solutions" to your "artistic problems".
Don't let technology get in the way of your creativity!
The main issue is a communication problem between our Mac Pros (with ATTO cards) fibred to the Facilis Terrablock storage system. The Facilis website mentions problems with 10.5.6:
Apple OS version 10.5.6 is not supported by Facilis Technology on older Mac Pro workstations that use the Expansion Slot utility. The ATTO Celerity card normally in a x4 slot will default to a x1 slot and cause problems with fibre channel communication.
Until further notice, the workaround for this problem is to revert the workstation back to 10.5.5.
Facilis Technology Support
After working w/ our IT dept and Facilis, we were able to troubleshoot around the error and get our drives back online... The cause of error is still unknown, but problem is temporarily fixed. We will try to weather the storm until Facilis updates rather than revert our OS. But probably not prepared to go to 10.5.7 until Facilis is able to comply with the newer OS versions. For months, we ran 10.5.6 w/out knowing of the issue and didn't have problems until now... Hopefully, its not a frequent type of error.