How do I customize a ringtone?

[dbence4]

Formula to customize ringtone

I'm looking at rooting my HTC One (m7) (recently updated to android 5.0.2 and sense 6).

I was hoping that somebody would be able to tell me if there was a way to customize my ringtones based on the phone numbers calling me.

So for example, I forward my work phone to my cell all the time. I want to make sure that all the phone calls from work numbers ring differently than my regular ringtone.
I should add, that I work in an airport, and I receive calls from all the gates, bridges and check in counters. It's probably about 200 different phone numbers, and I really don't have the time/energy to program them all into my contacts.

So what I would like is something that looks at the incoming phone number, and if it is 403.735.xxxx it triggers the specific ringtone.

Is this something that I could do if my phone was rooted? And if so, does anybody know how to make this happen?

Thanks for any and all help on this.