Unless Tivo has changed policy you must crack the signed boot-loader system before you can install a modified kernel. The last time I did this it was a very involved process that would be nearly impossible for a non-Linux user. On the other hand, most people keep the stock kernel and crack the root password and install their own processes and software. Though that is not the same as doing the kernel hack.
Tivoisation is called that because Tivo locked the kernel to the hardware. Without cracking the boot loader encryption you can't load a custom kernel and that is what RMS has a problem with and why he called it Tivioisation, in that it's free software but there are software and hardware restrictions that prevent the replacement of the kernel on that system even though it's open source and GPL.