How to have conditional default value for Subscribed By attribute?

Hi everyone,
Would like to do something like the following:
When an attribute such as Request Type is set to "Broke/Fix" then set a Subscribed By attribute to a default value of "User List X", else if the Request Type attribute is set to "Enhancement" then set the Subscribed By attribute to a default value of "User List Y".
Any guidance would be appreciated. Thanks in advance!
Jeff
One answer

Default values fire only once. A type can be changed and then? I am pretty sure that the requirement has something to do with email notification. I don't think JavaScript will help. A follow up action could be done but I think the whole use case is not well defined and will likely not be satisfactory. More here:
Comments
Donald Nong
May 17 '17, 11:24 p.m.What you described is a typical "calculated value" provider. While you can have a custom "Subscriptions" type attribute, I doubt that you can change the value of the built-in Subscribed By attribute.
Jeffrey Burke
May 18 '17, 9:39 a.m.Thanks Donald!