Permanently connecting templates to entries
I guess I'd refactor this and introduce different entry types for your section. Besides being able to "lock" each entry type to a specific template (→ "How can I give each Entry Type its own template?"), you can also have the CP fields (slightly) different. Maybe it makes sense to have extra fields for your special entries, if it doesn't, just add the same fields to each entry type. 

Another option would be to have a dropdown field to select the template, but I like that the entry type dropdown is in the right panel in the CP.