Incremental meshing on existing tetrahedron meshes about netgen HOT 3 CLOSED

Not trivially, but you can merge existing surface (and volume) meshes or mesh domains seperately. For example salome has built this in in their interface to netgen.
Do you need to keep the structure of the mesh for some reasons?

from netgen.

Yes, I have a fine-grained head mesh (http://www.parralab.org/nyhead/) and we want to add electrodes around it. An electrode is modeled with a small cylinder whose top face is used as the boundary conditions. Electrical current flows into this bc which accounts for Neumann condition and we would like to conduct FEM simulation using ngsolve.

We would like to add electrodes at different locations and evaluate the performance of transcranial Electrical Stimulation (tES), for example, the depth or the active regions. We do not want to re-mesh the head each time we add electrodes but want to keep its structures, domains (materials) as is.

from netgen.

You can merge meshes and only partially mesh volume meshes. There is some documentation on these features here
https://ngsolve.org/docu/latest/netgen_tutorials/working_with_meshes.html

If you have a (partially meshed) mesh it should be possible to mesh the open domains using
mesh.GenerateVolumeMesh(only3D_domain_nr=domnr)

Hope this helps
Best

from netgen.