Many thanks for all the feedback.
The idea works for those applications that supports snapshots.
Like Sybase / SAP Adaptive Server Enterprise, Sybase / SAP IQ Server, DB2, MongoDB, MariaDB/MySQL, PostgreSQL etc..
Anyhow, back to the origin question:
Is there a way how to re-create the cow- format.
so that lvconvert --merge can be used.
Or by having lvconvert --merge to accept to read from a "cow file"
If that would be possible, than instant recovery would be possible from an external source, like a backup server.
Regards Tomas