How do i perform variable change substitution in either mupad or symbolic

I would like to convert an expression such as diff(Ur,r) to diff(Ur,NormR) where NormR(r,theta)=(RO-r)/(RO-Rw(theta)) with the symbolic functions of matlab.

the diff(Ur,r) is inside a larger expression and there are other derivatives with respect to r i would also like to change. Obviously on paper this is simple with a chain rule expansion to switch variables.

For example:

Continuity:=simplify(combine(eval(-rho*divu=ur/r*diff(r*rho,r)+ut/r*diff(rho,t)+uz*diff(rho,z))))

I would like to change the variable r to NormR which is a function of R in the above equation.