diff --git a/etrago/tools/modify_gas.py b/etrago/tools/modify_gas.py
new file mode 100644
index 000000000..4179d13e0
--- /dev/null
+++ b/etrago/tools/modify_gas.py
@@ -0,0 +1,208 @@
+# -*- coding: utf-8 -*-
+from pypsa.linopt import get_var, linexpr, join_exprs, define_constraints
+import numpy as np
+import pandas as pd
+
+
+def H2_feedin_modeling(n, gas_network_carrier, H2_share):
+    """Generate H2 feedin model
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    gas_network_carrier : str
+        Name of the pipeline network carrier.
+    """
+    mix_carrier = "CH4_H2_mix"
+    _feed_and_return_pipelines(n, gas_network_carrier)
+    _generate_gas_mix_buses(n, gas_network_carrier, mix_carrier)
+    _generate_gas_mix_pipelines(n, gas_network_carrier, mix_carrier)
+    _feedin_links(n, gas_network_carrier, mix_carrier)
+    _reconnect_links_loads(n, gas_network_carrier, mix_carrier)
+    _reconnect_stores(n, gas_network_carrier, mix_carrier)
+
+
+def _feed_and_return_pipelines(n, base_carrier):
+    """Duplicate pipeline infrastructure for feed and return pipelines.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    """
+    # duplicate links, change order, index and rewrite to network
+    links = n.links[n.links["carrier"] == base_carrier].copy()
+    links.rename(columns={'bus0': 'bus1', 'bus1': 'bus0'})
+    links.index = links.index + '_return'
+    n.import_components_from_dataframe(links, "Link")
+
+
+def _generate_gas_mix_buses(n, base_carrier, mix_carrier):
+    """Generate gas mixture buses for every gas bus.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    mix_carrier : str
+        Name of the carrier for gasmixture.
+    """
+    # copy gas buses, adjust carrier, rename index and write to network
+    buses = n.buses[n.buses["carrier"] == base_carrier].copy()
+    buses["carrier"] = mix_carrier
+    buses.index = buses.index + "_" + mix_carrier
+    n.import_components_from_dataframe(buses, "Bus")
+
+
+def _generate_gas_mix_pipelines(n, base_carrier, mix_carrier):
+    """Create pipelines for gasmixture.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    mix_carrier : str
+        Name of the carrier for gasmixture.
+    """
+    # duplicate existing pipelines, adjust carrier, index and buses
+    pipelines = n.links[n.links["carrier"] == base_carrier].copy()
+    pipelines["carrier"] = mix_carrier
+    pipelines.index = pipelines.index + "_" + mix_carrier
+    pipelines["bus0"] = pipelines["bus0"] + "_" + mix_carrier
+    pipelines["bus1"] = pipelines["bus1"] + "_" + mix_carrier
+    n.import_components_from_dataframe(pipelines, "Link")
+
+
+def _feedin_links(n, base_carrier, mix_carrier):
+    """Create links for feedin of both gases into mixture bus.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    mix_carrier : str
+        Name of the carrier for gasmixture.
+    """
+    # select gas buses, generate link from gas bus to respective mix bus
+    buses = n.buses[n.buses["carrier"] == base_carrier]
+    links = pd.DataFrame()
+    links["bus0"] = buses.index
+    links["bus1"] = buses.index + "_" + mix_carrier
+    links["p_nom"] = np.inf
+    links["link_id"] = buses.index + "_" + base_carrier + "_input"
+    links["carrier"] = base_carrier + "_feedin"
+    n.import_components_from_dataframe(links.set_index("link_id"), "Link")
+
+    # change the original H2 feedin target buses to mixture buses
+    H2_feedin_filter = n.links["carrier"] == "H2_feedin"
+    n.links.loc[H2_feedin_filter, "bus1"] += mix_carrier
+
+
+def _reconnect_links_loads(n, base_carrier, mix_carrier, no_mixture=["CH4_to_H2"]):
+    """Reconnect all outgoing links and loads from pipeline network.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    mix_carrier : str
+        Name of the carrier for gasmixture.
+    no_mixture : list, optional
+        Links, that do not use mixture, by default ["CH4_to_H2"]
+    """
+    # create mixture (base carrier + mixture carrier) output buses
+    buses_base = n.buses[n.buses["carrier"] == base_carrier]
+    buses = buses_base.copy()
+    buses["carrier"] = mix_carrier + "_output"
+    buses.index = buses.index + "_output"
+    n.import_components_from_dataframe(buses, "Bus")
+
+    # reconnect links
+    # include all links with bus0 in base gas carrier
+    m1 = n.links["bus0"].isin(n.buses[n.buses["carrier"] == base_carrier].index)
+    # exclude pipelines
+    m2 = n.links["carrier"] != base_carrier
+    # exclude links to mix buses
+    m3 = ~n.links["bus1"].isin(n.buses[n.buses["carrier"] == mix_carrier].index)
+    # exlucde links which require pure base carrier
+    m4 = ~n.links["bus1"].isin(n.buses[n.buses["carrier"] == base_carrier].index)
+    m5 = ~n.links["carrier"].isin(no_mixture)
+    n.links.loc[m1 & m2 & m3 & m4 & m5, "bus0"] += "_" + mix_carrier + "_output"
+
+    # reconnect loads
+    m1 = n.loads["carrier"] == base_carrier
+    n.loads.loc[m1, "bus"] += "_" + mix_carrier + "_output"
+
+    # create links to output buses
+    links = pd.DataFrame()
+    links["labels"] = buses.index + "_" + base_carrier + "_input"
+    # source bus is the base carrier
+    links["bus0"] = buses_base.index
+    # target bus is the output bus
+    links["bus1"] = buses.index
+    links["p_nom"] = np.inf
+    links["carrier"] = base_carrier
+    n.import_components_from_dataframe(links.set_index("labels"), "Link")
+
+    # copy data with mixture_carrier as source bus
+    links = links.copy()
+    links["labels"] = buses.index + "_" + mix_carrier + "_input"
+    links["bus0"] += "_" + mix_carrier
+    links["carrier"] = mix_carrier
+    n.import_components_from_dataframe(links.set_index("labels"), "Link")
+
+
+def _reconnect_stores(n, base_carrier, mix_carrier):
+    """Reconnect all stores.
+
+    Parameters
+    ----------
+    n : pypsa.Network
+        Network to be modified.
+    base_carrier : str
+        Name of the pipeline network carrier.
+    mix_carrier : str
+        Name of the carrier for gasmixture.
+    """
+    # select and duplicate all CH4 stores
+    # reconnect copied stores to mix_buses
+    stores = n.stores[n.stores["carrier"] == base_carrier].copy()
+    stores["carrier"] = mix_carrier
+    stores.index = stores["bus"] + " " + mix_carrier
+    stores["bus"] += "_" + mix_carrier
+    n.import_components_from_dataframe(stores, "Store")
+
+
+def compressor_modeling():
+    """
+    """
+    pass
+
+
+def H2_pipeline_modeling():
+    """
+    """
+    pass
+
+
+def H2_retrofit_modeling():
+    """
+    """
+    pass
+
+
+def generate_extra_functionalities():
+    """
+    """
+    pass