Re: How to save specific (or current) outfit as the bathing outfit?

You should be able to do that in Create A Sim (CAS).

Click on a mirror or dresser and Change Sim to enter CAS. Other methods for entering CAS will also work. Once you are in CAS, click on the Sim's clothes to bring up outfits, then click on the floatie symbol to select Swimwear. Choose the outfit that you want for that category. You can add more outfits by clicking on the triangle above the floatie symbol and then the + symbol, up to a maximum of 5. You can do the same for other categories and other Sims in the same household. Once you are finished choosing outfits, click on the checkmark (Done) at the bottom of the screen to save, and return to the game. Click on the X (Cancel), instead of the checkmark, if you decide not to save your changes.