You can get away with it. But, there definatly is a good chance to throw a CEL. I did. The bigger TMIC really changes your boost properties. IE: more airflow, cooler charge, different boost pressure drop across the IC, and your ECU may have to try to adjust to it. My car was consistantly pulling 22.5 psi on a 20 psi protuned map. But, I still got the CEL. My tuner said it would be just a couple adjustments that wouldn't take much to fix. So, I went back and got retuned with the Walboro installed. Oh yeah, also changed my bcs....just because I was going back for a tune.
378awhp/373wtq Custom Dom 3 & CBRD tuned 2006 STI.
"When in doubt...flat out" - Colin McRae