SamyGO

It's CI+ device. It's easy to rool it back IF you upgraded your flash ONCE.
You can use alternative flash bank which is unrestricted firmware.

If you upgraded your flash with restricted firmwares (after feb 2010 releases) more than once, or if you bought TV with restricted firmware, than you cannot use "alternative firmware way".

It's possible to flash TV with older firmwares again but it's dangerous than other way because of authld. You might brick of your device if you make some mistakes.
You needed to calculate hash keys for your flashed firmware partitions for deactivate authld.
Please look wiki pages for detailed info.

You can run those programs via Children Menu.Do you tried?
Copy those programs to Children Menu than run...
Please search on forum to learn technique.(you can also use google search at main page, which is better)

Since your TV is CI+, I don't recommend you a downgrade (yet).

I don't know what is problem with your keyboard. My USB keyboard working without problem.
you can inspect problem by rooting your TV.
Access from telnet and inspect kernel messages for error.
You can also try to load required kernel modules by hand.

AFAIK, every keyboard need to be compatible with BIOS or you cannot edit your bios settings of your PC with that keyboard, right?
So linux drivers uses this compatibility. So I don't expect if any problem arise on keyboard. But on mouse is different story since it doesn't required to be bios compatible.
So any keyboard will be work. But don't know if that track-pad recognized. At worst scenario, you needed to find a driver for your keyboard track pad which compatible with linux kernel in your TV. I think it will be work with %90 probability unless it's Bluetooth compatible modem/keyboard. But Arris69 has also include bluetooth stack to SamyGO expansion pack, afaik.

Use FFB 0.6.2. Its safe enough (with common risk of firmware flashing)
Also here is all needed Apps included - activate alternative firmware as well. But only if you're sure.