I tend to think of the term "jailbreak", in this metaphor, as "breaking down your jail" by consciously recognizing its component parts, thereby giving you the ability to interact with and change the way you perceive the world.
I've tried to deal with the confusion surrounding this metaphor in the past, but I don't know how successful I was. All I know is that I butted in on one of the famous LMNO-vs-Ratatosk debates.
Basically, I argued that the confusion over "breaking out" of the BIP (which is referred to in the very first part of the BIP pamphlet) is the result of actually having two metaphors with the same name. Somehow this dual metaphor sneaked its way into the publication without anyone complaining, and I rather like that even though, or perhaps because, it causes this confusion. I'm going to try to restate my position.
The first Black Iron Prison I will deal with is the "larger" BIP. This is the BIP that consists largely of biological limits on our perception, and this is the one where we "rearrange the bars" but cannot escape because to "escape" this BIP implies nothing short of omniscience. We as humans are biologically incapable of, say, perceiving all wavelengths of light simultaneously or hearing sounds out of our fairly limited range. However, the other component of this BIP is belief systems, which are highly changeable. Therefore this larger BIP cannot be broken out of, but it can be altered for the purpose of changing one's perception of reality to some extent.
The second Black Iron Prison is the "smaller" BIP. This is the BIP that we are invited to "escape" in the pamphlet, and it's also the BIP that (hypothetically) one escapes by comprehending the psychobabble about Reality Grids in the Principia. This is the BIP of ignorance, since one cannot change one perceptions of reality if one never grasps the idea that one's perceptions are limited.
Corollary to all this is that when we "break out" of the smaller BIP, then we are free to tinker with the belief systems that comprise part of the larger BIP. Your mileage may vary, and certain people seem to be more focused about either the larger BIP or the smaller one.
I did all these fancy metal gymnastics, and then Nigel wrote the above quote and made the idea of two BIPs unnecessary.