MAYBE: Add function to change default

[EmilHvitfeldt]

having a function that take a defaulted 0 integer and turn it into a defaulted 1 integer as an example.

To be used in situations where all defaults should be identical, such as in coerce_to_sparse_matrix()

[EmilHvitfeldt]

same idea for length, positions or values. I have a feeling it will be faster to update an existing vector than copy all the things over. but will have to run some benchmarks