To a large extent, yes. Head position (varies with helmet), back curve, hand and arm positions etc. We measure the number of watts saved by various combinations of rider position/rider equipment (helmets/skinsuits etc) in real time and pop the number up on the on-bike screen in real time. Currently moving to doing this out on the road (following validation on indoor velodromes and wind tunnels), kind of fun being able to see this position saves 10 watts, that one saves 15 watts but is too uncomfortable to hold for long etc.

There are been a lot of fuss about that in the UK time trial scene with rider mounting 3d printed parts behind their arms and calves to lower their drag.

The biggest gain of TT/Triathlon bikes is moving your position from an upright seated position to a lower and narrower position, so "modding" the rider ;-)

After that, skinsuits, helmets and overshoes are usually the best bang-for-your-buck (in no particular order) in terms of aero gains.

I love blowing past other riders who have spent ridiculous sums on their bikes optimizing for weight with carbon and titanium setups when they could have had better performance by just eating better and losing a few more pounds. Beyond a minimal threshold, it's not the machine, it's the motor that counts.

Yes but there are lots of rules about that too, and lots of workarounds to those rules, of varying ethical dubiousness.

...hence aero helmets, socks, leg shaving....so, yes.