That's for PAL unfortunately so I don't think that will work for you (values should though, just not the base code).
The only way I know of to get the 7-speed is to change the car's name to the Subaru Pleo, buy it's 7-spd transmission, revert to your car's original name, then set it using the codes below)
I've never found a value that worked for the 7-speed on PAL :/ Although 6 is way more than enough for this game's physics
"Transmission
801cd5a0 ????
&Choice
$00F4 6 speed
$0841 4 speed
This used with the PAL version of the gear ratio modifiers (because when making hybrids, going into the settings menu will revert to original, so if you want to mod the added gears, you have to use this):
"Reverse
801cd5cc ????
?0000-FFFF
"1ERE
801cd5ce ????
?0000-FFFF
"2NDE
801cd5d0 ????
?0000-FFFF
"3EME
801cd5d2 ????
?0000-FFFF
"4EME
801cd5d4 ????
?0000-FFFF
"5EME
801cd5d6 ????
?0000-FFFF
"6EME
801cd5d8 ????
?0000-FFFF
"7EME
801cd5da ????
?0000-FFFF
"FINALE
801cd5dc ????
?0000-FFFF
"AUTO.
801cd5de ????
?0000-FFFF