What has happened in the past is that Tesla will revalue the whole order. If the total order price drops, Tesla have passed on the saving. If the order price has increased, Tesla has absorbed the increase. This is for Tesla changes only and not necessarily the case where price changes outside their control has changed, ie grants. But they have tried.
Note the term, whole order. Within this, there may also be individual item price increases. These will still occur but will be captured in the total order value. So you may see individual item price increases but the total order will be lower or no higher. Looking from the periphery of these price changes, I think there has also been a recent base price increase, so this increase needs to be thrown into the mix when it comes to calculating the whole order price.
This does however affect any customer changes made to the order. This will cause the whole order to be repriced but in this case, Tesla will not honour the whole order parity, so your order price may increase.
tl;dr - historically, no need to do anything. As long as you do not change your order, Tesla will honour the whole order price of your old order in case of a Tesla instigated price rise or give you a lower total order price if prices go down.