No because Moodle is built on top of a database and there's no way to merge incremental changes from one database into another like this.
I would:
- Try to capture all the changes that you're aware of – all the obvious ones and the ones you can remember – into a list.
- Keep a copy of the 3.10.1 sites as test sites.
- Upgrade the 3.4.9 sites to 3.10.1.
- Apply the changes from the list.
- As you become aware of changes that were missed from the list refer to the 3.10.1 test sites and apply the changes as needed.
Moodle has a configuration changes report which may help you find settings that were changed when developing the 3.10.1 site.
When making copies of Moodledata (not the database), a file copy tool that copies incremental changes only, such as Rsync, makes copying file data much quicker.