So definitely no way to set up a personalized text tone for a contact, which stinks; however, it is possible to differentiate a text tone from all other notifications. Choose your general notifications tone under 'Sounds and Vibration'. Then under 'Notifications' scroll down and select 'Messages'. From there, select 'New Messages' and make changes under 'Sound'. Now your general notification tone will be different from your text tone. Hope this helped!
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