This statement in the manual refers specifically to the IceTV login and related subscription detection on SKIPPA (account and AutoSkip), and prohibits hacking / decompiling of the firmware in any way - particularly in terms of this subscription detection mentioned above.
First of all, the term "conditional access" has a very specific meaning in the STB/PVR industry, so the choice of that terminology is a bit unfortunate. You may wish to revise it.
However, moving onto a more important matter, I think you may have a few issues here...
As far as I can tell from all the info on the forums, the box is based on a Broadcom STB reference design. That means it's running a Linux kernel, which is licensed under the GPL. It's impractical (actually close to impossible) to build a modern Broadcom STB/PVR (especially one that can run Opera), without GPL, LGPL and other Open Source components. That means that not only is it perfectly OK for anyone to take apart the firmware and see how it works, but it also means that you have to provide the source code to the GPL and LGPL components, including any modifications you have made. On top of that, the LGPL also requires you to ship the code in such a way that anyone can replace the LGPL components with whatever alternative version they choose and still be able to rebuild a fully working firmware. That means that your code must be supplied in a format that is readily usable by anyone wishing to modify the firmware. Most commonly this is done by shipping proprietary code as a set of shared libraries with corresponding header files that provide a public API.
Of course, your intellectual property is still protected by your copyrights, but you can not restrict the rights that the end users have as a result of you choosing to use GPL, LGPL or other Open Source code to build the product.
The GPL and LGPL licenses (and probably other licenses, such as the JPEG library code) also require you to publish the licensing terms in your manuals. Even the most permissive licenses, such as 3-clause BSD License, require you to publish the license terms. You should probably talk to your OEM about third party and Open Source licensing compliance and get them to furnish you with the required licenses and corresponding code.