Const vector of non-const objects

The C++ const-correctness concept is IMO way overrated. What you just discovered is one of the big limitations it has: it doesn't scale by composition. To be able to create a const vector of non-const objects you need to implement your own vector type. Note that for example even the standard library had to introduce new types for const_iterators.

My suggestion is to use const-correctness where you are forced to, and not everywhere you can. In theory const correctness should help programmers, but comes at a very high cost because of the syntax and is very primitive (just one bit, doesn't scale by composition, even requires code duplication).

Also in my experience this alleged big help is not really that big... most of the errors it catches are related to the const-correctness machinery itself and not to program logic.

Ever wondered why most languages (including ones designed after C++) didn't implement this idea?

Rather than passing the vector into the function, do what the standard library does and pass a pair of iterators instead.

virtual void ModifyPreComputedCoeffs ( std::vector < IndexCoeffPair_t >::iterator & model_begin, std::vector < IndexCoeffPair_t >::iterator & model_end )