[Tony Curcio]

The guys who extend the vent tube forward are correcting a specific problem- the float level is high (on purpose), and raw fuel sloshes up and out the vent tube under hard acceleration, then it seeps into the primary venturi. So, yes, this could effect performance under some circumstances. Only one way to find out for sure, try it. You can always put the tube back in.

As for its legality, that seems like a matter of interpretation, so you may as well ask your division tech. A strict constructionist will probably say no, but it doesn't make the car go faster, so who knows.