diff --git a/README.md b/README.md
index 80846ef..c101647 100644
--- a/README.md
+++ b/README.md
@@ -229,8 +229,9 @@ Defaults are in `flatten.hooks`.
     This is useful for customizing when files should be sent to a host instance and when they should be opened
     in a new one.
 
-- `hooks.pre_open`: `fun(opts: Flatten.PreOpenContext)`
+- `hooks.pre_open`: `fun(opts: Flatten.PreOpenContext): Flatten.Config?`
   - Called before opening files.
+  - Returned config, if any, will be merged with the global config (for this file only).
 
   - `Flatten.PreOpenContext`:
     - `data`: `any`
diff --git a/lua/flatten/core.lua b/lua/flatten/core.lua
index e7388d3..4f14132 100644
--- a/lua/flatten/core.lua
+++ b/lua/flatten/core.lua
@@ -71,6 +71,13 @@ local function parse_argv(argv)
   return pre_cmds, post_cmds
 end
 
+local function mergeConfig(new, default)
+  if new == nil then
+    return default
+  end
+  return vim.tbl_deep_extend("keep", new, default)
+end
+
 ---@param opts { argv: string[], response_pipe: string, guest_cwd: string }
 ---@return boolean
 function M.run_commands(opts)
@@ -142,9 +149,6 @@ function M.edit_files(opts)
   local force_block = opts.force_block
   local argv = opts.argv
   local config = require("flatten").config
-  local hooks = config.hooks
-  local focus_first = config.window.focus == "first"
-  local open = config.window.open
   local data = opts.data
   local quickfix = opts.quickfix
 
@@ -166,9 +170,15 @@ function M.edit_files(opts)
     return false
   end
 
-  hooks.pre_open({
-    data = data,
-  })
+  config = mergeConfig(
+    config.hooks.pre_open({
+      data = data,
+    }),
+    config
+  )
+  local hooks = config.hooks
+  local focus_first = config.window.focus == "first"
+  local open = config.window.open
 
   for _, cmd in ipairs(pre_cmds) do
     vim.api.nvim_exec2(cmd, {})
diff --git a/lua/flatten/init.lua b/lua/flatten/init.lua
index 078be84..cb419f5 100644
--- a/lua/flatten/init.lua
+++ b/lua/flatten/init.lua
@@ -124,7 +124,8 @@ local Flatten = {}
 ---config.nest_if_no_args is respected.
 ---@field should_nest? fun(host: integer):boolean
 ---Called before a nested session is opened.
----@field pre_open? fun(opts: Flatten.PreOpenContext)
+---Retuened config is merged with global config for this file
+---@field pre_open? fun(opts: Flatten.PreOpenContext): Flatten.Config?
 ---Called after a nested session is opened.
 ---@field post_open? fun(opts: Flatten.PostOpenContext)
 ---Called when a nested session is done waiting for the host.