There is no way to merge files and it can be a headache exporting and importing the data accurately so the new company would allow current transaction processing but you would need to end up back entering it again.  Overall not ideal but might be your only option.  If you create a new company you can copy from an existing company and I would suggest using that feature as it may help make things possibly to export and import once caught up.  

That's what I would do. When you catch up the old company to the 2024 year, then export the 2024 data out and import into the older company. That is less time consuming and whatever does not import, enter manually. You'll have to export out the Chart of Accounts, Vendor, Customer and Inventory Item lists in case you don't have them in the older company.