Transfer data from an apple id to a new apple id

When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. If possible, also set up Family Sharing  between the IDs to keep access to your apps/purchases. 

 How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.       

What to do after you change your Apple ID or password - Apple Support.      

Family Sharing.         

Family Sharing - Set up.        

You can’t. Purchases and downloads are forever tied to the Apple ID that made them. There is no way to transfer them.

For iCloud Data such as photos and files, you would need to manually download them from iCloud and move them to the new account.

In general, you should not be creating new accounts unless it is absolutely necessary. Your Apple ID is the key to all things Apple and tied to all the services and purchases you have. It should always be kept up to date and accessible and used on all the devices you own.