Well.. not that simple..
The RR only allows 8K ROM banked in at a time. In 16K (GAME+EXROM=LOW) mode, the ROM at $8000 is simply mirrored at $A000. RR does however allow you to map in both RR RAM and ROM at the same time, thus giving you 16K.
If you e.g. have 2*8K and want the lower 8K (bank0) at $8000, and the upper 8K (bank1) at $A000, you could copy the lower 8K ROM of Bank0 to the lower 8K RR RAM at bank1 and then switch to RR Bank1 upon completion. This would give you the desired result.
To write to the RR RAM however, you need to switch to Ultimax mode and you would have to switch between banks 0 and 1 all the time, so your "copy code" would need to be located somewhere <$1000 in C64 RAM or you could use the AllowBank Bit and stuff it in e.g. $deXX.
An example:
Code:
$0800:
lda #$ff
sta $fc
lda #$9f
sta $fe
lda #0
sta $fb
sta $fd
tay
ldx #$1f
$0812:
lda #$23 ;RR-RAM at $8000, Bank0, Ultimax
sta $de00
lda ($fb),y ;Read from RR-Bank0 ROM
sta $02
lda #$2b ;RR-RAM at $8000, Bank1, Ultimax
sta $de00
lda $02
sta ($fd),y ;Write to RR-Bank1 RAM
iny
bne :-
dec $fc
dec $fe
dex
bpl :-
lda #$29 ;RR-RAM at $8000, Bank1, + RR-ROM Bank1 at $A000
sta $de00
jmp FANCY_CART_CODE
There are of course a million variations to complete the same task, and probably a lot smarter ones than this, but if you get the idea, I think you're good to go ,-)