Ideally yes....clean tank n new coil or rewick....if the coil is still good...or you feel like experimenting just run the new liquid through your empty tank and old coil...you will taste the old liquid for a while though till the new liquid comes through....some liquid flavours are powerful though and will linger longer than others.
Yeah, I find fruits swap out pretty quick. Some sweets/lolly flavours refuse to budge and you have to change the coil. I generally will pour out the juice from the tank, wipe out the glass, wipe the coil and fill it up. Sometimes completely different flavours mash for a half a tank and can be weird but end up OK. Other times no. Can be trial and error but after a while you know what to expect.
I vape the tank dry. If it is the end of the night, I take everything apart soak in hot water for 10 minutes and let it dry overnight.
If not I vape dry, and a little of the new juice, roll it around and vape dry, top with new juice.
If the flavour you want to change is vile then pour away, wash tank and chuck coil. That’s how I had to cope after trying Heisenberg (spelling?) the most disgusting flavour ever.....to me!