The ability to edit templates is mSecure 6 as long as you have an Essentials account. No features have been removed from mSecure 6 if you have an Essentials account, which is what you have as V5 Pro license holder.
First, how are you trying to modify or create new Templates? On an iOS device, simply go to the Settings, then tap "Edit Templates." There, you will be able to either edit any of your existing templates or create new templates, the same way you created new or edited existing "Types" in mSecure 5.
The one thing you can't do in v6 with an Essentials account is use the advanced field settings at the record level, but those field settings didn't exist in mSecure 5, so you aren't losing any functionality in V6. You can still add fields to a record, change the name of the fields, and, if you remove the data from the field label and the field itself, that field will be deleted from the record when you save the changes. Again, you have lost no functionality in V6 Essentials that you had in V5 Pro.
No problem at all Michael! There are some pretty big changes in V6, so some of the features that were in V5 are not handled in the exact same manner. It's hard to bring all those changes to light, so it's not uncommon that we get questions about this type of thing =) Also, thank you for the RTFM acronym! I can't believe I had never seen that one before. I had to look it up and then had a good laugh!
Take care, and please let me know if you need further assistance.