...without ruining anything?

I hear the combo can run an extension speaker load of 8ohms. I guess it automatically switches?

But with my line 6 cab it says 8ohms left and 8ohms right. In parentheses it says (4 ohms this input only) under the left speaker input. the other just says eight.

Can I assume that the other can have just one input and be 8 ohms still? So could I put my Classic 30 on this cab using the right input at 8 ohms mono?

Thanks in advance.
I think it is trying to say that if you are going to just use one input, to use the left and run it at 4 ohms