diff --git a/python/ctsm/site_and_regional/neon_arg_parse.py b/python/ctsm/site_and_regional/neon_arg_parse.py
index 3aa619aad3..7317c947fb 100644
--- a/python/ctsm/site_and_regional/neon_arg_parse.py
+++ b/python/ctsm/site_and_regional/neon_arg_parse.py
@@ -195,6 +195,17 @@ def get_parser(args, description, valid_neon_sites):
         choices=["v1", "v2", "v3"],
     )
 
+    parser.add_argument(
+        "--xmlchange",
+        help="""
+                Any xmlchanges (e.g., CLM_CO2_TYPE=constant,CCSM_CO2_PPMV=500)
+                [default: %(default)s]
+                """,
+        required=False,
+        type=str,
+        default=None,
+    )
+
     args = parse_args_and_handle_standard_logging_options(args, parser)
 
     if "all" in args.neon_sites:
@@ -254,4 +265,5 @@ def get_parser(args, description, valid_neon_sites):
         args.rerun,
         args.no_input_data_check,
         args.user_version,
+        args.xmlchange,
     )
diff --git a/python/ctsm/site_and_regional/neon_site.py b/python/ctsm/site_and_regional/neon_site.py
index 7978eac2ed..82ef7adf05 100755
--- a/python/ctsm/site_and_regional/neon_site.py
+++ b/python/ctsm/site_and_regional/neon_site.py
@@ -68,6 +68,7 @@ def run_case(
         rerun=False,
         experiment=False,
         no_input_data_check=False,
+        xmlchange=None,
     ):
         """
         Run case.
@@ -116,6 +117,7 @@ def run_case(
             rerun,
             experiment,
             no_input_data_check,
+            xmlchange,
         )
 
     def modify_user_nl(self, case_root, run_type, rundir, site_lines=None):
diff --git a/python/ctsm/site_and_regional/run_neon.py b/python/ctsm/site_and_regional/run_neon.py
index d4ded645b7..2d9346d49e 100755
--- a/python/ctsm/site_and_regional/run_neon.py
+++ b/python/ctsm/site_and_regional/run_neon.py
@@ -196,6 +196,7 @@ def main(description):
         rerun,
         no_input_data_check,
         user_version,
+        xmlchange,
     ) = get_parser(sys.argv, description, valid_neon_sites)
 
     if output_root:
@@ -242,4 +243,5 @@ def main(description):
                 rerun=rerun,
                 experiment=experiment,
                 no_input_data_check=no_input_data_check,
+                xmlchange=xmlchange,
             )
diff --git a/python/ctsm/site_and_regional/tower_site.py b/python/ctsm/site_and_regional/tower_site.py
index 7f83b29663..33b36b7613 100644
--- a/python/ctsm/site_and_regional/tower_site.py
+++ b/python/ctsm/site_and_regional/tower_site.py
@@ -264,6 +264,7 @@ def run_case(
         rerun,
         experiment,
         no_input_data_check,
+        xmlchange,
     ):
         """
         Run case.
@@ -411,6 +412,12 @@ def run_case(
             if not rundir:
                 rundir = case.get_value("RUNDIR")
 
+            if xmlchange:
+                xmlchange_list = xmlchange.split(",")
+                for setting in xmlchange_list:
+                    setting_split = setting.split("=")
+                    case.set_value(*setting_split)
+
             self.modify_user_nl(case_root, run_type, rundir)
 
             case.create_namelists()