src/streamer/localize/localize.py

@@ -30,6 +30,10 @@ def localize_shard(
 
                     value = placement.value or marker
 
+                    if placement.overwrites or (
+                        placement.dimension not in position
+                        and placement.dimension not in private_position
+                    ):
                         if dimension.propagate:
                             position[placement.dimension] = value
                         else:

src/streamer/localize/repository_configuration.py

@@ -15,6 +15,7 @@ class MarkerPlacement(BaseModel):
     if_with: set[str] = set()
     dimension: str
     value: str | None = None
+    overwrites: bool = True
 
 
 class Marker(BaseModel):

test/test_localize.py

@@ -85,3 +85,147 @@ class TestLocalize:
                 "timesheet": "coding",
             },
         )
+
+    def test_overwrites_true_propagated_dimension_overwrites_existing_value(self):
+        config = RepositoryConfiguration(
+            dimensions={
+                "project": Dimension(display_name="Project", propagate=True),
+            },
+            markers={
+                "A": Marker(
+                    display_name="A",
+                    placements=[MarkerPlacement(dimension="project", value="a")],
+                ),
+                "B": Marker(
+                    display_name="B",
+                    placements=[
+                        MarkerPlacement(dimension="project", value="b", overwrites=True)
+                    ],
+                ),
+            },
+        )
+
+        stream_file = StreamFile(
+            file_name="20260131-210000 Test File.md",
+            shard=Shard(start_line=1, end_line=1, markers=["A", "B"]),
+        )
+
+        assert localize_stream_file(stream_file, config) == LocalizedShard(
+            moment=datetime(2026, 1, 31, 21, 0, 0, 0),
+            markers=["A", "B"],
+            tags=[],
+            start_line=1,
+            end_line=1,
+            children=[],
+            location={"file": stream_file.file_name, "project": "b"},
+        )
+
+    def test_overwrites_false_propagated_dimension_does_not_overwrite_existing_value(
+        self,
+    ):
+        config = RepositoryConfiguration(
+            dimensions={
+                "project": Dimension(display_name="Project", propagate=True),
+            },
+            markers={
+                "A": Marker(
+                    display_name="A",
+                    placements=[MarkerPlacement(dimension="project", value="a")],
+                ),
+                "B": Marker(
+                    display_name="B",
+                    placements=[
+                        MarkerPlacement(
+                            dimension="project", value="b", overwrites=False
+                        )
+                    ],
+                ),
+            },
+        )
+
+        stream_file = StreamFile(
+            file_name="20260131-210000 Test File.md",
+            shard=Shard(start_line=1, end_line=1, markers=["A", "B"]),
+        )
+
+        assert localize_stream_file(stream_file, config) == LocalizedShard(
+            moment=datetime(2026, 1, 31, 21, 0, 0, 0),
+            markers=["A", "B"],
+            tags=[],
+            start_line=1,
+            end_line=1,
+            children=[],
+            location={"file": stream_file.file_name, "project": "a"},
+        )
+
+    def test_overwrites_true_non_propagated_dimension_overwrites_private_value(self):
+        config = RepositoryConfiguration(
+            dimensions={
+                "label": Dimension(display_name="Label", propagate=False),
+            },
+            markers={
+                "A": Marker(
+                    display_name="A",
+                    placements=[MarkerPlacement(dimension="label", value="a")],
+                ),
+                "B": Marker(
+                    display_name="B",
+                    placements=[
+                        MarkerPlacement(dimension="label", value="b", overwrites=True)
+                    ],
+                ),
+            },
+        )
+
+        stream_file = StreamFile(
+            file_name="20260131-210000 Test File.md",
+            shard=Shard(start_line=1, end_line=1, markers=["A", "B"]),
+        )
+
+        assert localize_stream_file(stream_file, config) == LocalizedShard(
+            moment=datetime(2026, 1, 31, 21, 0, 0, 0),
+            markers=["A", "B"],
+            tags=[],
+            start_line=1,
+            end_line=1,
+            children=[],
+            location={"file": stream_file.file_name, "label": "b"},
+        )
+
+    def test_overwrites_false_non_propagated_dimension_does_not_overwrite_private_value(
+        self,
+    ):
+        config = RepositoryConfiguration(
+            dimensions={
+                "label": Dimension(display_name="Label", propagate=False),
+            },
+            markers={
+                "A": Marker(
+                    display_name="A",
+                    placements=[
+                        MarkerPlacement(dimension="label", value="a", overwrites=True)
+                    ],
+                ),
+                "B": Marker(
+                    display_name="B",
+                    placements=[
+                        MarkerPlacement(dimension="label", value="b", overwrites=False)
+                    ],
+                ),
+            },
+        )
+
+        stream_file = StreamFile(
+            file_name="20260131-210000 Test File.md",
+            shard=Shard(start_line=1, end_line=1, markers=["A", "B"]),
+        )
+
+        assert localize_stream_file(stream_file, config) == LocalizedShard(
+            moment=datetime(2026, 1, 31, 21, 0, 0, 0),
+            markers=["A", "B"],
+            tags=[],
+            start_line=1,
+            end_line=1,
+            children=[],
+            location={"file": stream_file.file_name, "label": "a"},
+        )