I don't use cartos with one
juice then another unless I want to vape the blend of flavors. I will do it with prefilled cartos and top off with something that blends well. For blank cartos I use 1 carto for the same flavor over and over. I used dripping or a cart to try flavors (actually a Joye 306 atty and its cart which together are the size of a carto). Then if I like something enough, it gets a carto. Else I just vape it occasionally at home w/ drip or cart.
Some people are successful with cleaning, drying and reusing cartos but some are not successful. After a carto has be well-used, I stick it in a bag and plan to try a cleaning but have not yet.
Juice can evaporate some in cartos because some juices have distilled water or PGA to adjust the flow, and I think nicotine can dissipate somewhat, etc. If you keep the condoms on it should help prevent that.
I don't use the condom method for filling. One former proponent of that method now thinks it shortens the life of a carto. And I like to see inside, see the air channel is straight and free of juice and that no juice is pooled above the stuffing. I usually use a plastic or delrin drip tip as a mouthpiece on stuffing-type cartos so I can just pull that and add a bit of juice if it needs it.