Change work of mailer class in Redmine?

Question

Ruby on Rails

There is a task to add an event (sending SMS) with the priority of the task immediate.
I got to /redmine/app/models/mailer.rb and
see this
: subject => "[#{issue.project.name} - #{issue.tracker.name} ##{issue.id}] (#{issue. status.name}) #{issue.subject}"
i.e. issue.priority method should issue.priority? and if it is immediate, then run a third-party script with parameters
itself in ruby
​​version 2.5.2.stable is not strong