Yep. Much of the AR's appeal and why it has become the hottest selling rifle in the country is because of its modular construction. They are just so easy to customize.Agreed with what's been said.
You have to remember---AR's are the Lego of the gun world.
Anybody with ANY mechanical ability, the capacity to follow
simple instructions and a couple of cheap tools can make an
AR anything they want. HUGE aftermarket in any parts you
might desire, 15 seconds to swap to a different upper.
I know a LOT of people with AR's, and I'll bet less than 5 of
them are still exactly as they came from the manufacturer.