diff --git a/rendercv/data_models.py b/rendercv/data_models.py
index a28cef6..54cfa80 100644
--- a/rendercv/data_models.py
+++ b/rendercv/data_models.py
@@ -25,6 +25,7 @@ import json
 import re
 import ssl
 import pathlib
+import warnings
 
 import pydantic
 import pydantic_extra_types.phone_numbers as pydantic_phone_numbers
@@ -35,6 +36,9 @@ from .themes.moderncv import ModerncvThemeOptions
 from .themes.sb2nov import Sb2novThemeOptions
 from .themes.engineeringresumes import EngineeringresumesThemeOptions
 
+# disable Pydantic warnings:
+warnings.filterwarnings("ignore")
+
 # Create a custom type called RenderCVDate that accepts only strings in YYYY-MM-DD or
 # YYYY-MM format:
 # This type is used to validate the date fields in the data.
@@ -1126,6 +1130,69 @@ class RenderCVDataModel(RenderCVBaseModel):
             return theme_data_model
 
 
+def set_or_update_a_value(
+    data_model: pydantic.BaseModel | dict | list,
+    key: str,
+    value: Any,
+    sub_model: pydantic.BaseModel | dict | list = None,
+):
+    """Set or update a value in a data model for a specific key. For example, a key can
+    be `cv.sections.education.3.institution` and the value can be "Bogazici University".
+
+    Args:
+        data_model (pydantic.BaseModel | dict | list): The data model to set or update
+            the value.
+        key (str): The key to set or update the value.
+        value (Any): The value to set or update.
+        sub_model (pydantic.BaseModel | dict | list, optional): The sub model to set or
+            update the value. This is used for recursive calls. When the value is set
+            to a sub model, the original data model is validated. Defaults to None.
+    """
+    # recursively call this function until the last key is reached:
+
+    # rename `sections` with `sections_input` since the key is `sections` is an alias:
+    key = key.replace("sections.", "sections_input.")
+    keys = key.split(".")
+
+    if sub_model is not None:
+        model = sub_model
+    else:
+        model = data_model
+
+    if len(keys) == 1:
+        # set the value:
+        if isinstance(model, pydantic.BaseModel):
+            setattr(model, key, value)
+        elif isinstance(model, dict):
+            model[key] = value
+        elif isinstance(model, list):
+            model[int(key)] = value
+        else:
+            raise ValueError(
+                "The data model should be either a Pydantic data model, dictionary, or"
+                " list.",
+            )
+
+        data_model.model_validate(data_model.model_dump(by_alias=True))
+    else:
+        # get the first key and call the function with remaining keys:
+        first_key = keys[0]
+        key = ".".join(keys[1:])
+        if isinstance(model, pydantic.BaseModel):
+            sub_model = getattr(model, first_key)
+        elif isinstance(model, dict):
+            sub_model = model[first_key]
+        elif isinstance(model, list):
+            sub_model = model[int(first_key)]
+        else:
+            raise ValueError(
+                "The data model should be either a Pydantic data model, dictionary, or"
+                " list.",
+            )
+
+        set_or_update_a_value(data_model, key, value, sub_model)
+
+
 def read_input_file(
     file_path: pathlib.Path,
 ) -> RenderCVDataModel:
diff --git a/tests/test_data_models.py b/tests/test_data_models.py
index 5aa204d..f8c8148 100644
--- a/tests/test_data_models.py
+++ b/tests/test_data_models.py
@@ -2,6 +2,7 @@ from datetime import date as Date
 import json
 import pathlib
 import os
+import re
 import shutil
 
 import pydantic
@@ -59,6 +60,52 @@ def test_format_date(date, expected_date_string):
     assert dm.format_date(date) == expected_date_string
 
 
+@pytest.mark.parametrize(
+    "key, value",
+    [
+        ("cv.phone", "+905555555555"),
+        ("cv.email", "test@example.com"),
+        ("cv.sections.education.0.degree", "PhD"),
+        ("design.page_size", "a4paper"),
+    ],
+)
+def test_set_or_update_a_value(rendercv_data_model, key, value):
+    dm.set_or_update_a_value(rendercv_data_model, key, value)
+
+    # replace with regex pattern:
+    key = re.sub(r"sections\.([^\.]*?)\.(\d+)", 'sections_input["\\1"][\\2]', key)
+
+    assert eval(f"rendercv_data_model.{key}") == value
+
+
+@pytest.mark.parametrize(
+    "key, value",
+    [
+        ("cv.phones", "+905555555555"),
+        ("cv.emssdsail", ""),
+        ("cv.sections.education.99.degree", "PhD"),
+        ("dessssign.page_size", "a4paper"),
+    ],
+)
+def test_set_or_update_a_value_invalid_keys(rendercv_data_model, key, value):
+    with pytest.raises((ValueError, KeyError, IndexError, AttributeError)):
+        dm.set_or_update_a_value(rendercv_data_model, key, value)
+
+
+@pytest.mark.parametrize(
+    "key, value",
+    [
+        ("cv.phone", "+9999995555555555"),
+        ("cv.email", "notanemail***"),
+        ("cv.sections.education.0.highlights", "this is not a list"),
+        ("design.page_size", "invalid_page_size"),
+    ],
+)
+def test_set_or_update_a_value_invalid_values(rendercv_data_model, key, value):
+    with pytest.raises(pydantic.ValidationError):
+        dm.set_or_update_a_value(rendercv_data_model, key, value)
+
+
 def test_read_input_file(input_file_path):
     # Update the auxiliary files if update_testdata is True
     if update_testdata: