1. I do not expect significant issues, but also I may have a different definition of significant. I see two potential problems that do not seem insurmountable, so you may be willing to try:
- First, searching for "lower_boundary" in `bld/namelist_files/namelist_definition_ctsm.xml` I see that you cannot use_groundwater_irrigation with lower_boundary_condition = 3. Maybe that's not a problem at all.
- Second, there's a possibility that the model will go through an adjustment in response to the new setting. If so, you may decide that you need to drop that part of the simulation, or whatever you think is best for your experiments.
2. I do not have recent experience with these parameters, so I will let others chime in here.