Dropdown with not valid values


I have a main table with several fields plus a field called activity which is in relation with a table called activity
When creating or updating the main table the user uses a dropdownlist to select the activity
The application is now running since several years and there are many activities that are no longer used for new entries in the main table
There is a field in the table activity which is called “enabled” and at this moment all activities are enabled.
Now we wish to disable some old activities.

My question is :
When we display the main table, is it possible to show all values, even disabled activities.
But if the user uses the dropdownlist in the main table for the activity we wish to see only enabled activities.

Thanks if any idea