Change the label of a region / some elements

Dear all,

If we have a large mesh Th and a small mesh Ths on top of it, we know interpolate() or
transferMat() can provide the interpolation matrix between these two meshes. My questions are:

  1. can we print the elements’ label of Th that are covered by Ths (in order to compute the interpolation matrix, I believe we already have these information)?
  2. can we easily change these elements’ label?

Thank you very much in advance!