If the aw ban sunsets will all of the pre ban extras fit on my post ban ar? Like flash hiders?

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Never underestimate the power of stupid people in large groups.

As to whether or not they fit is a question that is best left to your gunsmith.  Some adjustments MAY be needed, and some probably WILL be.  

Legally, those features will be allowed to be added to your rifle if the ban sunsets and no replacement legislation is enacted.

The simplest way to add the missing features is to just put a new upper assembly on the rifle and call it a day.   Actually adding a bayonet lug will require a new sight base to be installed, and this is definitely a job for a good gunsmith.   Adding a flash hider will also require gunsmith skills and tools.

A different stock is easy enough, though.

CJ