Can I configure triggering mechanisms (to run CI pipeline) as I want?

Currently, when I push my local branch to my branch on the repo server and then click “New merge request” and then click “Compare branches and continue”, it will trigger CI pipeline to run. When I merge my branch on the repo server with master, it will trigger CI pipeline to run again. Can I configure (enable/disable) this triggering function anytime? In general, can I configure triggering mechanism as what I want? For example, force to trigger CI process starting unit test (not from merge request) w/o changing YAML file. In other words, what kinds of mechanisms (besides changing YAML file) will trigger GitLab Runner to run YAML file? Thank you for your time and help!

Note: my GitLab version 11.1.1, self-managed by another team.