Yes, probably it's the safest thing on plesk to do. I upgraded to mailenable pro 3 and then 4, and never had any problems. It's all automatically installed and everthing started working better then before after each of my upgrade.
There is only on thing that you should know. After the install finishes, you should go to Plesk Component Management and REFRESH the page. otherwise plesk still thinks that you are using mailenable standart and does not let you use mailenable webmail client.
After the refresh rightaway plesk understands that new mailenable is working and you can go.
Thanks.