Hmm, it doesn't look like there's a simple way to change from +1 to +8 olives within the 3 code limit the real Game Genie hardware allows. The problem is the the flag set when you're picking up an olive (memory address $006B set to #$01) is also the value placed in the accumulator to be added to the olive total. Unfortunately, the INC command was used instead of LOAD #$01.

What CAN be done, however, is using Game Genie codes that trick the game into thinking that you're picking up the 100th olive, and it sets it back to the max of 99.

Battle of Olympus NES (USA version)
GGVISPAO + VAVIVPZP + OIVINPIV picking up one olive counts as 99

For reference, here's the programming:

$8E09:E6 6B INC $6B = #$01 //picked up an olive

$D8A4:A5 6B LDA $6B = #$01
$D8A6:F0 22 BEQ $D8CA
$D8A8:20 60 D9 JSR $D960 //jsr add olive to total

$D960:A4 E1 LDY $E1 = #$01
$D962:C9 00 CMP #$00
$D964:18 CLC
$D965:10 12 BPL $D979
$D967:65 E0 ADC $E0 = #$00
$D969:10 1E BPL $D989
$D96B:88 DEY
$D96C:30 07 BMI $D975
$D96E:18 CLC
$D96F:69 0A ADC #$0A
$D971:30 F8 BMI $D96B
$D973:10 14 BPL $D989
$D975:A9 00 LDA #$00
$D977:F0 0F BEQ $D988
$D979:65 E0 ADC $E0 = #$00
$D97B:C9 0A CMP #$0A
$D97D:90 0A BCC $D989
$D97F:E9 0A SBC #$0A
$D981:C8 INY
$D982:C0 0A CPY #$0A
$D984:90 F5 BCC $D97B
$D986:A9 09 LDA #$09 //max 99 olives
$D988:A8 TAY
$D989:85 E0 STA $E0 = #$00 //olives ones place
$D98B:84 E1 STY $E1 = #$01 //olives tens place
$D98D:60 RTS

The Game Genie set GGVISPAO + VAVIVPZP + OIVINPIV creates the following patch:
$D965:4C 86 D9 JMP $D986