diff --git a/scripts/phase0/build_spec.py b/scripts/phase0/build_spec.py
index fa7d1fb68..98b1cad78 100644
--- a/scripts/phase0/build_spec.py
+++ b/scripts/phase0/build_spec.py
@@ -2,13 +2,14 @@ import sys
 import function_puller
 
 
-def build_spec(sourcefile, outfile):
+def build_phase0_spec(sourcefile, outfile):
     code_lines = []
     code_lines.append("""
     
 from typing import (
     Any,
     Callable,
+    Dict,
     List,
     NewType,
     Tuple,
@@ -41,7 +42,7 @@ Any = None
 Store = None
     """)
 
-    code_lines += function_puller.get_lines(sourcefile)
+    code_lines += function_puller.get_spec(sourcefile)
 
     code_lines.append("""
 # Monkey patch validator get committee code
@@ -78,7 +79,16 @@ def hash(x):
         ret = _hash(x)
         hash_cache[x] = ret
         return ret
-    """)
+
+# Access to overwrite spec constants based on configuration
+def apply_constants_preset(preset: Dict[str, Any]):
+    global_vars = globals()
+    for k, v in preset:
+        global_vars[k] = v
+
+    # Deal with derived constants
+    GENESIS_EPOCH = slot_to_epoch(GENESIS_SLOT)
+""")
 
     with open(outfile, 'w') as out:
         out.write("\n".join(code_lines))
@@ -86,5 +96,6 @@ def hash(x):
 
 if __name__ == '__main__':
     if len(sys.argv) < 3:
-        print("Error: spec source and outfile must defined")
-    build_spec(sys.argv[1], sys.argv[2])
+        print("Usage: <source phase0> <output phase0 pyspec>")
+    build_phase0_spec(sys.argv[1], sys.argv[2])
+
diff --git a/scripts/phase0/function_puller.py b/scripts/phase0/function_puller.py
index 2cd0139c5..d0f3f66f1 100644
--- a/scripts/phase0/function_puller.py
+++ b/scripts/phase0/function_puller.py
@@ -1,7 +1,8 @@
 import sys
+from typing import List
 
 
-def get_lines(file_name):
+def get_spec(file_name) -> List[str]:
     code_lines = []
     pulling_from = None
     current_name = None
diff --git a/test_libs/config_helpers/README.md b/test_libs/config_helpers/README.md
new file mode 100644
index 000000000..184482082
--- /dev/null
+++ b/test_libs/config_helpers/README.md
@@ -0,0 +1,19 @@
+# ETH 2.0 config helpers
+
+`preset_loader`: A util to load constants-presets with.
+See [Constants-presets documentation](../../configs/constants_presets/README.md).
+
+Usage:
+
+```python
+configs_path = 'configs/'
+
+...
+
+import preset_loader
+from eth2spec.phase0 import spec
+my_presets = preset_loader.load_presets(configs_path, 'main_net')
+spec.apply_constants_preset(my_presets)
+```
+
+WARNING: this overwrites globals, make sure to prevent accidental collisions with other usage of the same imported specs package.
diff --git a/test_libs/config_helpers/preset_loader/__init__.py b/test_libs/config_helpers/preset_loader/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/test_libs/config_helpers/preset_loader/loader.py b/test_libs/config_helpers/preset_loader/loader.py
new file mode 100644
index 000000000..043c58805
--- /dev/null
+++ b/test_libs/config_helpers/preset_loader/loader.py
@@ -0,0 +1,18 @@
+from typing import Dict, Any
+
+from ruamel.yaml import (
+    YAML,
+)
+from pathlib import Path
+from os.path import join
+
+
+def load_presets(configs_dir, presets_name) -> Dict[str, Any]:
+    """
+    Loads the given preset
+    :param presets_name: The name of the generator. (lowercase snake_case)
+    :return: Dictionary, mapping of constant-name -> constant-value
+    """
+    path = Path(join(configs_dir, 'constant_presets', presets_name+'.yaml'))
+    yaml = YAML(typ='safe')
+    return yaml.load(path)
diff --git a/test_libs/config_helpers/requirements.txt b/test_libs/config_helpers/requirements.txt
new file mode 100644
index 000000000..e441a474b
--- /dev/null
+++ b/test_libs/config_helpers/requirements.txt
@@ -0,0 +1 @@
+ruamel.yaml==0.15.87
diff --git a/test_libs/config_helpers/setup.py b/test_libs/config_helpers/setup.py
new file mode 100644
index 000000000..90ad94ee4
--- /dev/null
+++ b/test_libs/config_helpers/setup.py
@@ -0,0 +1,9 @@
+from distutils.core import setup
+
+setup(
+    name='config_helpers',
+    packages=['preset_loader'],
+    install_requires=[
+        "ruamel.yaml==0.15.87"
+    ]
+)
diff --git a/test_libs/gen_helpers/setup.py b/test_libs/gen_helpers/setup.py
index 88b971bf3..5de27a6db 100644
--- a/test_libs/gen_helpers/setup.py
+++ b/test_libs/gen_helpers/setup.py
@@ -2,7 +2,6 @@ from distutils.core import setup
 
 setup(
     name='gen_helpers',
-    version='1.0',
     packages=['gen_base'],
     install_requires=[
         "ruamel.yaml==0.15.87",