Change does not happen sub consciously. There are various quotes about practicing something 10,000 times to perfect it, including Bruce Lee. In cycling this attitude is required whether it is to improve the smoothness of your pedaling or cornering.
For TT riders the importance of of obtaining and holding an aero position cannot be understated. You pay good money to get be aero tested but if you do not practice riding in that position you will not make the gains you expect to make. there is no silver bullet to gaining speed, rather it is derived from good technical advice combined with lots of quality practice. Do not just turn up to your next TT after a test thinking you will now go faster. The chances are you will actually be slower.
Practice is about helping your body adapt to the position. First, the chances are your position will be lower and tighter, probably involving a shoulder shrug and head being held lower. You will not do this subconsciously, so need to keep reminding yourself to move into the correct position. This may mean remembering several aspects at once concerning position of your head, hands, shoulders, bottom and legs.
Secondly if you have moved into a lower position the movement of your hip flexors and glutes will have changed, you may find soreness in your muscles as they learn to hold or push through new angles. It will take time for your muscles to adjust and for you to put out the same power and levels of endurance. This may mean some additional strength work in the gym as well.
Thirdly, a new position may require better bike handling skills. As you get narrower on your bars your bike will become less stable, more difficult to corner with and susceptible to cross winds.
All of these issues can be overcome and you can successfully move to your new position and faster times but it does require the right amount of practice. Fabian Cancellara said the secret to his TT success was that he trained every week on his TT bike, unlike many in the peleton who just turned up hoping to do well. In short he was comfortable in his TT position and could use all his power throughout the whole ride.
You too can do this but need to make it a training goal, an ideal one for recovery days and steady intervals.