Some CEL's can effect your cars performance. When your ECU detects a problem it will throw up the CEL and throw itself into a default mode. It may try to compensate for the problem which can effect other systems and sensors on the car which in turn can damage those systems. It's good to keep posted on sites like this and read what other people have done to their rides so that you don't make the same mistake or know what mods do or don't cause problems. No matter what you want to do, someone has always done it before you.
As far as warranties go, better to not go in the dealership with a **** load of mods or they might decide not to warranty you. I have this statement from Subaru:
"We do NOT recommend the installation of any aftermarket part into any of our vehicles. Doing so may affect your warranty, but only on related failures. Any problems caused by the installation or performance of an aftermarket product will not be covered by your warranty; thus, you would be responsible for the repairs. "
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