I'm sure customs would be very skeptical at first but hopefully if they test a whole bunch of the guns coming in and they all pass they may relax a bit on that retailer and stuff will go through faster.
once it's in you hands if you change out the spring thats up to you. and as far as cost it's either a bit more or no new gear at all if the trend continues plus your getting pre upgraded internals so it's not like nothing is coming from the extra money.
to make this effective at all it would have to be done by volume retailers because if individuals ordered 1 gun at a time it's going to get tested for sure.
I'd much rather get my PAL myself but this is another option if the need should arise