A method for converting between related plans is needed
A plan that is cloned from another plan is "related" to the first plan. Any questions in the two plans that are identical (type and values), can be easily converted between. There will no doubt be questions in either plan that are not in the other, or that otherwise needs to be converted by hand (like essay question to integer..) so the conversion cannot be 100% but every question counts.
What's needed for this is that all clonable models have a field pointing back to the original row. (This should also make cloning easier..)
With that in: a way to run through the existing plan, look up the answers in the old template and map them to the new.