If you're changing accounts but want to keep your existing content, you'll want to take your Snapchat memories with you. Unfortunately, it will take a workaround to do this. You will need to export everything to your device then upload it again. But, if you want it to appear in memories, you'll need to put it in the 'My Eyes Only' folder. Then, tap the three vertical lines in the upper right-hand corner and tap the option to remove the snap from the secret folder. It will then appear in your memories.