The core of your question seems to be:
“i want to understand how can i change the “Strategy” value with a variable that can put the right value into this field just after %UserRole_<variable>’”
My approach here would be to simply create a microflow that will check the incoming variable and retrieve the corresponding user role (based on a series of yes/no decisions to check a string or on an enumeration representing the desired user role).
After retrieving you would simply set the user role by updating the ‘System.UserRoles’ association of your user (check if you need ‘Set’ or ‘Add’)