Extension on a ServiceType in a Schedule

I’m looking for advice on the best way to implement something. Here is our use case: the Schedule object currently contains an array of 0…many ServiceTypes. We need to add some more information around how this ServiceType applies to this Schedule. Example: Schedule A references ServiceType 1, but only for new patients. Schedule B references ServiceType 1, but only for existing patients.

Would it be acceptable to place an extension on each ServiceType instance included in the array that makes up a Schedule? Here’s an example array from a Schedule that contains only one ServiceType:

“serviceType”: [
“coding”: [
“code”: “xyz”,
“display”: “Annual Physical”,
“system”: “/CodeSystem/ServiceTypes”
“text”: “Annual Physical”,
“extension”: {
“valueString”, “NEW”

Are there better or more compliant ways to accomplish something like this? Thank you!