What is the best way to remove a knot from a (univariate) spline?

In my problem, I have a planar curve, i.e., a 2-valued univariate spline function s. I insert k-1 times a value in the knot sequence with fnrfn(s, repmat(u0, [1, k-1]) and I modify slightly the resulting coefficients. If I wanted to express the modified spline in the space of the original one, what would be the best way?

I am thinking in something like:

k = s.order;
sNew = fnrfn(s, repmat(u0, [1, k-1]);
sNew.coefs = something(sNew.coefs);
cheb = chbpnt(s.knots, s.order);
spapi(s.knots, cheb, fnval(sNew, cheb))

Regards,

Unai