No, it should simply be updated so that the module allows up to 16 character usernames. The module should continue to generate 8 character usernames. Since clients cannot create or change their usernames, the only way you could run into trouble is if a staff member attempts to create an account with a longer that accepted username. In that case, I suspect cPanel would throw an error. It solves the issue where cPanel accounts created outside of Blesta with longer usernames cannot currently be added to Blesta.
The documentation @ https://documentation.cpanel.net/display/SDK/WHM+API+1+Functions+-+createacct
and this blog entry @ http://blog.cpanel.com/update-to-recent-database-prefixing-post/
indicate that usernames longer than 8 characters are conditional on database prefixing.
Should this be a module row setting instead?