diff --git a/stack_orchestrator/data/stacks/fixturenet-optimism/deploy/commands.py b/stack_orchestrator/data/stacks/fixturenet-optimism/deploy/commands.py
index fa757cf5..2e67da77 100644
--- a/stack_orchestrator/data/stacks/fixturenet-optimism/deploy/commands.py
+++ b/stack_orchestrator/data/stacks/fixturenet-optimism/deploy/commands.py
@@ -14,7 +14,6 @@
 # along with this program.  If not, see <http:#www.gnu.org/licenses/>.
 
 from stack_orchestrator.deploy.deployment_context import DeploymentContext
-from ruamel.yaml import YAML
 
 
 def create(context: DeploymentContext, extra_args):
@@ -23,17 +22,12 @@ def create(context: DeploymentContext, extra_args):
     # deterministic-deployment-proxy contract, which itself is a prereq for Optimism contract deployment
     fixturenet_eth_compose_file = context.deployment_dir.joinpath('compose', 'docker-compose-fixturenet-eth.yml')
 
-    with open(fixturenet_eth_compose_file, 'r') as yaml_file:
-        yaml = YAML()
-        yaml_data = yaml.load(yaml_file)
-
     new_script = '../config/fixturenet-optimism/run-geth.sh:/opt/testnet/run.sh'
 
-    if new_script not in yaml_data['services']['fixturenet-eth-geth-1']['volumes']:
-        yaml_data['services']['fixturenet-eth-geth-1']['volumes'].append(new_script)
+    def add_geth_volume(yaml_data):
+        if new_script not in yaml_data['services']['fixturenet-eth-geth-1']['volumes']:
+            yaml_data['services']['fixturenet-eth-geth-1']['volumes'].append(new_script)
 
-    with open(fixturenet_eth_compose_file, 'w') as yaml_file:
-        yaml = YAML()
-        yaml.dump(yaml_data, yaml_file)
+    context.modify_yaml(fixturenet_eth_compose_file, add_geth_volume)
 
     return None
diff --git a/stack_orchestrator/deploy/deployment_context.py b/stack_orchestrator/deploy/deployment_context.py
index 239e9c5c..2ffc5b89 100644
--- a/stack_orchestrator/deploy/deployment_context.py
+++ b/stack_orchestrator/deploy/deployment_context.py
@@ -45,11 +45,14 @@ class DeploymentContext:
     def get_compose_dir(self):
         return self.deployment_dir.joinpath(constants.compose_dir_name)
 
+    def get_compose_file(self, name: str):
+        return self.get_compose_dir() / f"docker-compose-{name}.yml"
+
     def get_cluster_id(self):
         return self.id
 
-    def init(self, dir):
-        self.deployment_dir = dir
+    def init(self, dir: Path):
+        self.deployment_dir = dir.absolute()
         self.spec = Spec()
         self.spec.init_from_file(self.get_spec_file())
         self.stack = Stack(self.spec.obj["stack"])
@@ -66,3 +69,19 @@ class DeploymentContext:
             unique_cluster_descriptor = f"{path},{self.get_stack_file()},None,None"
             hash = hashlib.md5(unique_cluster_descriptor.encode()).hexdigest()[:16]
             self.id = f"{constants.cluster_name_prefix}{hash}"
+
+    def modify_yaml(self, file_path: Path, modifier_func):
+        """
+        Load a YAML from the deployment, apply a modification function, and write it back.
+        """
+        if not file_path.absolute().is_relative_to(self.deployment_dir):
+            raise ValueError(f"File is not inside deployment directory: {file_path}")
+
+        yaml = get_yaml()
+        with open(file_path, 'r') as f:
+            yaml_data = yaml.load(f)
+
+        modifier_func(yaml_data)
+
+        with open(file_path, 'w') as f:
+            yaml.dump(yaml_data, f)