String substitution: in string X, replace Y with Z.
  String padding: pad a string X to width at least Y with character Z.
  Dictionary update: given a dictionary D, set D[X] = Y.

The obvious solution here is to have a two-parameter function that serves as a product, combining two arguments into one (eg space-based stranding in APL-likes):

    (Y ⨂ Z) replace X
    (Y ⨂ Z) pad X
    D update X ⨂ Y