diff --git a/eden/mononoke/cmds/admin/main.rs b/eden/mononoke/cmds/admin/main.rs
index 62d6b16011..f2d6df5041 100644
--- a/eden/mononoke/cmds/admin/main.rs
+++ b/eden/mononoke/cmds/admin/main.rs
@@ -48,6 +48,7 @@ mod hg_sync;
 mod mutable_counters;
 mod phases;
 mod pushrebase;
+mod rebase;
 mod redaction;
 mod rsync;
 mod skiplist_subcommand;
@@ -86,6 +87,7 @@ fn setup_app<'a, 'b>() -> MononokeClapApp<'a, 'b> {
         .subcommand(subcommand_deleted_manifest::build_subcommand())
         .subcommand(derived_data::build_subcommand())
         .subcommand(rsync::build_subcommand())
+        .subcommand(rebase::build_subcommand())
         .subcommand(pushrebase::build_subcommand())
         .subcommand(subcommand_skeleton_manifests::build_subcommand())
 }
@@ -173,6 +175,9 @@ fn main(fb: FacebookInit) -> ExitCode {
             (rsync::RSYNC, Some(sub_m)) => {
                 rsync::subcommand_rsync(fb, logger, &matches, sub_m).await
             }
+            (rebase::REBASE, Some(sub_m)) => {
+                rebase::subcommand_rebase(fb, logger, &matches, sub_m).await
+            }
             (pushrebase::PUSHREBASE, Some(sub_m)) => {
                 pushrebase::subcommand_pushrebase(fb, logger, &matches, sub_m).await
             }
diff --git a/eden/mononoke/cmds/admin/rebase.rs b/eden/mononoke/cmds/admin/rebase.rs
new file mode 100644
index 0000000000..23c4ae9c45
--- /dev/null
+++ b/eden/mononoke/cmds/admin/rebase.rs
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This software may be used and distributed according to the terms of the
+ * GNU General Public License version 2.
+ */
+
+use anyhow::{anyhow, Error};
+use blobstore::Loadable;
+use clap::{App, Arg, ArgMatches, SubCommand};
+use fbinit::FacebookInit;
+use futures::{compat::Future01CompatExt, future::try_join};
+
+use blobrepo::save_bonsai_changesets;
+use cmdlib::{
+    args::{self, MononokeMatches},
+    helpers,
+};
+use context::CoreContext;
+use mononoke_types::{BonsaiChangesetMut, ChangesetId};
+use slog::Logger;
+
+use crate::error::SubcommandError;
+
+pub const ARG_DEST: &str = "dest";
+pub const ARG_CSID: &str = "csid";
+pub const REBASE: &str = "rebase";
+const ARG_I_KNOW: &str = "i-know-what-i-am-doing";
+
+pub fn build_subcommand<'a, 'b>() -> App<'a, 'b> {
+    SubCommand::with_name(REBASE)
+        .about(
+            "produce a bonsai changeset clone with p1 changed to a given value. \
+             DOES NOT RUN ANY SAFETY CHECKS, DOES NOT CHECK FOR CONFLICTS!",
+        )
+        .arg(
+            Arg::with_name(ARG_CSID)
+                .long(ARG_CSID)
+                .takes_value(true)
+                .required(true)
+                .help("{hg|bonsai} changeset id or bookmark name"),
+        )
+        .arg(
+            Arg::with_name(ARG_DEST)
+                .long(ARG_DEST)
+                .takes_value(true)
+                .required(true)
+                .help("desired value of the p1"),
+        )
+        .arg(
+            Arg::with_name(ARG_I_KNOW)
+                .long(ARG_I_KNOW)
+                .takes_value(false)
+                .help("Acknowledges that you understnad that this is an unsafe command"),
+        )
+}
+
+fn copyfrom_fixup(bcs: &mut BonsaiChangesetMut, new_parent: ChangesetId) {
+    for maybe_file_change in bcs.file_changes.values_mut() {
+        if let Some((_, ref mut cs_id)) = maybe_file_change.as_mut().and_then(|c| c.copy_from_mut())
+        {
+            *cs_id = new_parent;
+        }
+    }
+}
+
+pub async fn subcommand_rebase<'a>(
+    fb: FacebookInit,
+    logger: Logger,
+    matches: &'a MononokeMatches<'_>,
+    sub_matches: &'a ArgMatches<'_>,
+) -> Result<(), SubcommandError> {
+    if !sub_matches.is_present(ARG_I_KNOW) {
+        return Err(anyhow!("{} is required", ARG_I_KNOW).into());
+    }
+
+    args::init_cachelib(fb, &matches);
+    let ctx = CoreContext::new_with_logger(fb, logger.clone());
+    let repo = args::open_repo(fb, &logger, &matches).await?;
+
+    let cs_id = sub_matches
+        .value_of(ARG_CSID)
+        .ok_or_else(|| anyhow!("{} arg is not specified", ARG_CSID))?;
+
+    let dest = sub_matches
+        .value_of(ARG_DEST)
+        .ok_or_else(|| anyhow!("{} arg is not specified", ARG_DEST))?;
+
+    let (cs_id, dest) = try_join(
+        helpers::csid_resolve(ctx.clone(), repo.clone(), cs_id).compat(),
+        helpers::csid_resolve(ctx.clone(), repo.clone(), dest).compat(),
+    )
+    .await?;
+
+    let bcs = cs_id
+        .load(&ctx, repo.blobstore())
+        .await
+        .map_err(Error::from)?;
+    let mut rebased = bcs.into_mut();
+
+    if rebased.parents.is_empty() {
+        rebased.parents.push(dest);
+    } else {
+        rebased.parents[0] = dest;
+    }
+
+    copyfrom_fixup(&mut rebased, dest);
+
+    let rebased = rebased.freeze()?;
+    let rebased_cs_id = rebased.get_changeset_id();
+    save_bonsai_changesets(vec![rebased], ctx.clone(), repo).await?;
+
+    println!("{}", rebased_cs_id);
+    Ok(())
+}
diff --git a/eden/mononoke/mononoke_types/src/file_change.rs b/eden/mononoke/mononoke_types/src/file_change.rs
index 3cabc3246f..b78a73aa03 100644
--- a/eden/mononoke/mononoke_types/src/file_change.rs
+++ b/eden/mononoke/mononoke_types/src/file_change.rs
@@ -96,6 +96,10 @@ impl FileChange {
         self.copy_from.as_ref()
     }
 
+    pub fn copy_from_mut(&mut self) -> Option<&mut (MPath, ChangesetId)> {
+        self.copy_from.as_mut()
+    }
+
     #[inline]
     pub(crate) fn into_thrift_opt(fc_opt: Option<Self>) -> thrift::FileChangeOpt {
         let fc_opt = fc_opt.map(Self::into_thrift);