Hi Stefano,
Hope you are keeping well.
I would like to inform that old and new both HL keys are supported with EMS 7.4. As per my understanding, you want to check which HL key is compatible with your Entitlement (license). If yes, you need to use get info API and collect information from <configuration> and <key_type> tags. Now match this information with <capable_devices> list. If they match then you can use this HL key with corresponding Entitlement.
You can also customise get_info XML and per your requirement and parse the necessary data.
Thank You,
Anubhav