What I found is one line above the yen symbol is a line of 00's for the first 7 blocks. If you have the stock rims, it'll all be 00's. If you change (on my R32) to the white advan RGII, you'll see that the 01 block and 05 block will say 01. Now, change to the white RE30's and it'll say 03 and 03 in place for the 01's. So, I changed block 5 to 01, and I got chrome RGII's. I think it's possible, but it's going to be hard.
even if you input different numbers in the 01 and 05 blocks it will give you the set of rims in the 01 position front and rear, not two different rims.