Change Order of Database Backups
This seems to have been released in the latest version as below:

https://github.com/olahallengren/sql-server-maintenance-solution/issues/47

You'll need to add the list of database names to the @Databases parameter - but do check through the documentation and Github site for clarification.

As hot2use states above, master and model will never be covered by this script though, as they are not user databases.

I would suggest you give the documentation a read here.