Duc
when you remove the current CD and TD,your next season's car design will reset to 1 so keep in mind that.
I don't think this is the case, your car won't reset to 1 unless you move to another league.
Yes it will reset at the end of the season but not to 1. Your starting design at the beginning of next season will be determined by the star ratings and strength/weakness of the CDs you have employed in the team this season.
Every race your CD contributes to 1/17th of next season's design. So if you have already completed 9 races this season, next season's cars will already be 9/17ths (just over 50%) complete and any new CD you employ can only influence design by a maximum of 8/17ths.
So the closer you are to the end of the current season the less influence your new CD will have on next season starting design.