I wonder if this would help. ArcGIS Help (10.2, 10.2.1, and 10.2.2) Synchronizing a mosaic dataset is a good primary way to keep your mosaic datasets up to date with data and in sync with other connected mosaic datasets. (I have not used this).
I would test any scenario you are planning with a small subset of a mosaic. That is, take a copy or create another and see what replacing does (make sure to refresh). You may need to recreate the overviews since maybe things are not exactly alike. But mosaic datasets are also very powerful and you can have it point to both datasets and have a date/year assigned to each set to help with change detection or other analysis if you want.
ArcGIS Help (10.2, 10.2.1, and 10.2.2) What is a mosaic dataset help
I've done most of my mosaic dataset work in 10.3.x, and instead of using our SQL database, I use FGDBs and have the mosaic point to the raw imagery. No need for the overhead of SQL. This has been working much better than the mosaics we used to store in ArcSDE (MSSQL).
Another good resource on possible workflows and best practices
Image Management
The Image Management guide book is intended to support data managers responsible for managing and disseminating large collections of imagery to their user community. This user community may be limited to your organization, or it may include external users and the general public.