I usually have at least 9 atties in use at any given time sometimes more if I'm developing a juice flavor.
I usually have 3 of each consisting of Standards, Low Res and High Voltage. All 510's and 901's.
When I try out a new juice I always try to use a freshly flushed atty that is previously seasoned.
I also sometimes flush them between juice changes with pure grain alcohol, Ever Clear or vodka.
If your atty has flavor that hangs on and will not go away, you can soak them in Lemon juice for an hour and then flush it out with hot water followed by alcohol ( the alcohol get the water out faster when drying) or Coca cola over night and then flush it out and let it dry.
Sometimes if I'm out of vodka or Ever Clear, I'll simply flush the atty with unflavored VG and even vape a little of it.
To mark your atties you can use nail polish, car touch up paint or take one of your wife's nail files and cut a groove in the LR or HV's if they are unmarked.
When I'm switching between new flavors or testing new juice that I've created, I always drink water between vaping different flavors.
Just about anything you eat or drink can change the flavor and perception of the new juice you are evaluating. Coffee, fruit juices, cola, alcohol cheese, garlic, onions, candies mixed nuts etc etc etc will all change your initial impressions of a new juice.
When I'm just vaping and do not care about intensely evaluating the flavor, most of the time I don't do anything in particular I just vape until the old flavor dissipates and the new one taste right. If you prefer, keep a bottle of straight unflavored VG with you and drip some into your atty and then blow it out, vape a little of the unflavored and then try you new juice.