You should be able at least to work with variables in the data load editor using SET/LET. Have a look here
In case of version upgrade between service and feature release, you should uninstall previous version before install the new one. Do not forgot to manually delete the former certificates and the Qlik directory in C:\ProgramData
Hope this help
Thank you Vincenzo.
Only 3 question:
1) do you know if a service update is expected for using variable with interface?
2) It's better to install a feature release instead of service release?
3) For each new feature release i have to uninstall and install the new one or it's necessary to update with the new one?
Thanks very much.
Feature release includes all new available features whereas service release include only bug fixing between minor versions. Here you can find a more detailed doc
Avoiding to include all the last feature in the service release, they are at least in theory more stable. So it's really up to you which track better fit your needs.
You can just update service release between different versions.