In fact it didn't work :S

I had a way to do it in another script language:

int $input = 1017;
int $output = 1104;
int $step =1;
string $newcam = "new_cam";
string $fcam = "cam_sequence"; // each camera has the frame number in suffixe
scalar n;

// We duplicate the first camera of the sequence and rename it

select( "replace","${fcam}_${input}" );
cp( "all", "select" );
set( "name", "${newcam}" );

// We get the global position from each camera and we place a key at the frame

for(n=$input;n<=$output;n=n+$step)
{
frame $n;
set "$newcam:global", get "${fcam}_${n}:global";
key "$newcam:all";
}

But I don't know how to write it in mel :/