How set readOnly dynamically in record.js?

You should be able to adapt this Gist to do what you want:

Custom record view controller for setting entire record to read-only conditionally · GitHub

They key is to add the field name into the "noEditFields" array.

Do you know how I could apply this to the Revenue Line Item create subpanel view.  So when you are on an Opportunity Create screen and adding Revenue Line items via the subpanel I need to be able to make fields on that view read only or editable based on an on change event.

You should look at doing that via a custom dependency.

See here for more info:

http://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_7.8/Architecture/Sugar_Logic/Dependency_… 

http://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_7.6/Extension_Framework/Dependencies/ 

You should look at doing that via a custom dependency.

See here for more info:

http://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_7.8/Architecture/Sugar_Logic/Dependency_… 

http://support.sugarcrm.com/Documentation/Sugar_Developer/Sugar_Developer_Guide_7.6/Extension_Framework/Dependencies/