Add Contact Fields to Observer Rule

I find it strange that there is no way to run an observer rule on contact field updates. Or to take advantage of customer tags. These things would be very helpful and our critical for our internal processes. I would like to create custom drop down list fields that include membership information. Once a selection is made in the custom list, I would like a specific tag to be added to the contact. This seems quite simple, but I am not finding a way to do this. I am open to any suggestions from other Freshdesk Users. Hoping someone can guide me to a work around!