Replication of databases with specific prefix on master There are options to dynamically set variables on replication slaves, like replicate_wild_do_table and replicate_wild_ignore_table.
But, are there any options for replication master to dynamically set database names which begin with same prefix, and not repeating:

replicate-do-db=prefix_db1
replicate-do-db=prefix_other_db
replicate-do-db=prefix_third_database
...

in my.cnf.
Dynamically, no.

You could, however, write a SELECT against information_schema.TABLES to create the replicate-do-db list for subsequent manual (or programmatic) placement into the config file.

Are you really adding more databases frequently?

Would it be better to, instead, do replicate-ignore-db on the rest of the dbs?

Also, consider using binlog-... so that the filtering is done sooner (on the Master instead of on the Slave).  (Yes, there are valid reasons to delay the filtering until the Slave.)