One of the new features of the 1703 Sequencer mentioned in TechNet “What’s New” page involves templates.
No, Microsoft didn’t do what we asked to make it easy to always load the sequencer with a Template using a registry setting like we did in 4.x. But they did solve an issue that traps everyone when updating packages. The issue is that when you open up a package for update or editing, you must use the same settings that were used when creating the original package. This includes any changes in the tools/settings (this includes changes to the exclusion list), as well as checkboxes on the advanced tab of the sequencer editor. These are all things that are captured in a template file. When I train people in App-V Sequencing, I encourage them to save off a template file of any package that they make changes to these settings. This aids in updating packages and connection groups. I find this information is rarely properly documented by the packager.