If the 1st flavor you had in there was a lighter one, you can get away with it. The 1st couple vape sessions will taste like a mix between the two juices but eventually the new
juice will clear the old and you should be fine. Worst comes to worse, just pop the cap off of your juice bottle and pour it back in. But I do this pretty much any time I'd like to change flavors and it usually works out fine. (in MY oppinion) I HAVE heard a few people say they have to change the carto. Whatever. Works for me. If your on a serious budget, it'll be fine.