What do you think about extending built-in Redmine models?

Question

Ruby on Rails

Where did I even come up with this: in RM, roles are assigned to users through projects, but I would also like to have some global roles. If that is just an example, the question is not about a specific task, but about what is in the title. In principle, nothing prevents writing a migration in the plugin that adds the global_role_id field to the user model, but something stops me.
Are there any best practices/antipractices for this?