I wouldn't think so. It wouldn't be logically possible for a weapon to have both traits (non-piercing would be completely meaningless under the circumstances). It would be against  the spirit of the game to give a weapon a meaningless Trait just to reduce its' cost in Space Units. Either use a higher Tech Level if you need more room or give it a Trait such as Starship-Exclusive that carries a Penalty for the reduction in size.

Of course, the decision whether doing this is against the Rules is properly between you and whomever you are playing the game with. But if you spring too many surprises like this upon them, they are likely to find playing with you much less fun.

You'd still get the penalty to attacking fighter flights, I guess...  perhaps a more systemic solution would be a general rule that impacts of 0 or below always fail to inflict damage, even against targets with shields 0?  It could also serve to offset the power (and price) of the Ignores Shields & Increased Impact combo (though I'll be buggered if I can think of any weapon from any source that was Ignores Shields, Increased Impact, AND Non-Piercing...  and you'd probably rather have Starship-Exclusive in that third trait slot).