Well, you will be able to install game updates easily, as long as the updates don't require 3.56 or higher.
As for dlc, etc, you will not be able to transfer it from your online ps3 to your cfw ps3, it's simply not possible. There have been some demos that will install on cfw fine, but since the release of cfw, even demoes are needing PSN activation. There's nothing really we can do about that.
STOP! Before you ask questions... READ the first post! RTFFP = Read The F*cking First Post
Yes, A 3.55 "jb" (cfw) is available, no >3.55 "jb" or cfw yet.
Yes, A 3.55 downgrade is available. But not to lower than stock firmware! (What it came with)
No >3.55 downgrade is out there yet.