diff --git a/analyze-linuxcnc-wasm-blockers.sh b/analyze-linuxcnc-wasm-blockers.sh
index 57328c0..431554d 100755
--- a/analyze-linuxcnc-wasm-blockers.sh
+++ b/analyze-linuxcnc-wasm-blockers.sh
@@ -8,8 +8,8 @@ cd "$(dirname "$0")"
 # src/emc/rs274ngc/gcodemodule.cc, interp_namedparams.cc, interp_o_word.cc,
 # and the py*.cc module bindings; tooldata/native-backend blockers come from
 # src/emc/tooldata/tooldata_mmap.cc and tooldata_db.cc; native filesystem
-# blockers come from LinuxCNC RS274 sources such as interp_o_word.cc and
-# interp_write.cc.
+# coverage comes from LinuxCNC RS274 sources such as interp_o_word.cc
+# directory traversal and rs274ngc_pre.cc parameter-file replacement.
 linuxcnc_root=${LINUXCNC_ROOT:-../linuxcnc}
 manifest=${1:-linuxcnc-rs274-wasm-source-files.txt}
 
diff --git a/check-linuxcnc-wasm-blockers-source-map.sh b/check-linuxcnc-wasm-blockers-source-map.sh
index cb01b62..15f5722 100755
--- a/check-linuxcnc-wasm-blockers-source-map.sh
+++ b/check-linuxcnc-wasm-blockers-source-map.sh
@@ -30,6 +30,16 @@ grep -F '#include "pythonplugin/python_plugin.hh"' "$linuxcnc_root/src/emc/rs274
 grep -F 'dlopen' "$linuxcnc_root/src/emc/rs274ngc/interp_base.cc" >/dev/null
 grep -F 'opendir(direct)' "$linuxcnc_root/src/emc/rs274ngc/interp_o_word.cc" >/dev/null
 grep -F 'readdir(aDir)' "$linuxcnc_root/src/emc/rs274ngc/interp_o_word.cc" >/dev/null
+grep -F 'std::string tempfile = std::string(filename) + ".new";' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F '+ RS274NGC_PARAMETER_FILE_BACKUP_SUFFIX;' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'unlink(bakfile.c_str());' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'if(link(filename, bakfile.c_str()) < 0)' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'if(rename(tempfile.c_str(), filename) < 0)' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
 grep -F '#define TOOL_MMAP_FILENAME ".tool.mmap"' "$linuxcnc_root/src/emc/tooldata/tooldata_mmap.cc" >/dev/null
 grep -F 'int tool_mmap_creator(' "$linuxcnc_root/src/emc/tooldata/tooldata_mmap.cc" >/dev/null
 
@@ -153,6 +163,8 @@ for phrase in [
     "does not add CNC behavior",
     "must not become smoke parser behavior",
     "blocked `dlopen` and blocked tooldata-users remain empty",
+    'parameter-file replacement through `filename + ".new"`',
+    "O-word lookup and parameter-file replacement",
     "Python/Boost.Python remap paths remain tracked blockers",
     "./check-linuxcnc-wasm-blockers-source-map.sh",
     "does not interpret G-code",
diff --git a/docs/linuxcnc-wasm-blockers-source-map.md b/docs/linuxcnc-wasm-blockers-source-map.md
index b63dacf..6da3a50 100644
--- a/docs/linuxcnc-wasm-blockers-source-map.md
+++ b/docs/linuxcnc-wasm-blockers-source-map.md
@@ -18,6 +18,7 @@ a source-link/build guard only; it does not add CNC behavior and must not become
   replaced by the wasm-safe tooldata mmap backend shim.
 - `src/emc/rs274ngc/interp_o_word.cc` uses native directory traversal for
   O-word subroutine lookup; browser persistence remains OPFS-only.
+- `src/emc/rs274ngc/rs274ngc_pre.cc` implements LinuxCNC parameter-file replacement through `filename + ".new"`, `filename + ".bak"`, `unlink`, `link`, and `rename`; browser persistence remains OPFS-only.
 
 ## Manifest Coverage
 
@@ -44,7 +45,7 @@ a source-link/build guard only; it does not add CNC behavior and must not become
 | `core-dlopen-shimmed` | 1 | Core LinuxCNC `dlopen` user compiled with dlfcn shim. |
 | `core-tooldata-shimmed` | 1 | Core LinuxCNC tooldata source compiled with wasm tooldata shims. |
 | `core-tooldata-users-shimmed` | 2 | Core RS274/NML users of tooldata declarations. |
-| `core-native-fs-shimmed` | 16 | Core sources with native filesystem includes or calls covered by WASM shims. |
+| `core-native-fs-shimmed` | 16 | Core sources with native filesystem includes or calls covered by WASM shims, including O-word lookup and parameter-file replacement. |
 
 Required replacement set: