For my Test users the access token I can obtain has always the same scopes:
public_profile, basic_info, user_friends
I didn't find a way to modify the access token provided by the test users in the interface or via an API call.
Is there a simple way to modify the scope of the access token of a test user?
If what you want is to create some test access tokens for specific scopes and test different api functions with them, try this link: https://developers.facebook.com/tools/explorer/
There click the "Get Access Token" button, select any specific scope you want.
Sometimes you may see some checkboxes checked and you can't disable them by clicking. Then use the "Clear" button at the bottom.