Question: is there a way to have a custom text tone for a contact with my Nexus 5?
Answer: Below is instruction shared by one Nexus 5 owner, hope it works for you;
How to set a custom text tone for a contact on nexus 5:
Go into contacts and tap on the picture of the person, or the head
then tap on the small head on the right hand side, half way up the screen
then tap the symbol in the top right corner and a menu will drop down and you will see “set ringtone”