You can certainly direct your (POP) mail accounts to use the same folder. - File > Account Settings > Select account > Change Folder.
The from File > Account Settings > Data Files, set the default folder to that folder.
Copy any data you want from the now unused data file to the default then close the unused file.
If you copy your backup data file to the working folder (with Outlook Closed), you could open that one and set it as your default.

It it has the same name as one of your existing data files, then rename the existing file before copying the backup to the folder, and before you re-open Outlook. The backup should then open in place of the renamed file. You can open the renamed file to copy any information from it.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com