diff --git a/music21/common/objects.py b/music21/common/objects.py
index f6993e92fb..43fc7dc169 100644
--- a/music21/common/objects.py
+++ b/music21/common/objects.py
@@ -295,11 +295,13 @@ def _check_init(self, key: str|None = None) -> bool:
         if not getattr(self, 'frozen', True):
             return True
 
-        for st in inspect.stack():
-            if (st.frame.f_code.co_name in ('__init__', '__new__', '__setstate__')
-                    and 'self' in st.frame.f_locals
-                    and st.frame.f_locals['self'].__class__ == self.__class__):
+        frame = inspect.currentframe()
+        while frame is not None:
+            if (frame.f_code.co_name in ('__init__', '__new__', '__setstate__')
+                    and 'self' in frame.f_locals
+                    and frame.f_locals['self'].__class__ == self.__class__):
                 return True
+            frame = frame.f_back
         raise TypeError(f'This {self.__class__.__name__} instance is immutable.')
 
     def __setattr__(self, key: str, value: t.Any) -> None:
diff --git a/music21/meter/base.py b/music21/meter/base.py
index 673e750b87..ab2ed1edcf 100644
--- a/music21/meter/base.py
+++ b/music21/meter/base.py
@@ -35,7 +35,7 @@
 
 from music21.meter.tools import slashToTuple, proportionToFraction
 from music21.meter.core import (
-    MeterSequence, getMeterSequence, getMeterTerminal, makeSequence,
+    MeterSequence, getMeterSequence, getMeterTerminal,
 )
 
 environLocal = environment.Environment('meter')
@@ -1176,11 +1176,7 @@ def summedNumerator(self) -> bool:
     @summedNumerator.setter
     def summedNumerator(self, value: bool):
         if self.displaySequence is not None:
-            # displaySequence is immutable; swap in a copy with the new flag
-            ds = self.displaySequence
-            self.displaySequence = makeSequence(
-                ds.numerator, ds.denominator, ds._partition,
-                parenthesis=ds.parenthesis, summedNumerator=value)
+            self.displaySequence = self.displaySequence.modify(summedNumerator=value)
 
     # --------------------------------------------------------------------------
     # private methods -- most to be put into the various sequences.
@@ -1341,14 +1337,13 @@ def _setDefaultAccentWeights(self, depth: int = 3) -> None:
             weightValues[x + 1] = weightValueMin * pow(2, x)
 
         # set weights on accent partitions
-        self.accentSequence = self.accentSequence.partition([1] * accentCount)
-        for i in range(accentCount):
-            # get values from weightValues dictionary; terminals are
-            # immutable, so replace each with a re-weighted cached one
-            mt = self.accentSequence[i]
-            self.accentSequence = self.accentSequence.setIndex(
-                i, getMeterTerminal(
-                    mt.numerator, mt.denominator, weight=weightValues[weightInts[i]]))
+        accentSequence = self.accentSequence.partition([1] * accentCount)
+        weighted = []
+        for i, mt in enumerate(accentSequence):
+            # get values from weightValues dictionary
+            weighted.append(getMeterTerminal(
+                mt.numerator, mt.denominator, weight=weightValues[weightInts[i]]))
+        self.accentSequence = accentSequence.modify(partition=weighted)
 
     # --------------------------------------------------------------------------
     # access data for other processing
diff --git a/music21/meter/core.py b/music21/meter/core.py
index df9bc39d2b..64b189488f 100644
--- a/music21/meter/core.py
+++ b/music21/meter/core.py
@@ -118,9 +118,6 @@ def duration(self) -> FrozenDuration:
         '''
         return self._durationFromNumeratorDenominator(self.numerator, self.denominator)
 
-    def _reprInternal(self):
-        return str(self)
-
     def ratioEqual(self, other) -> bool:
         '''
         Compare the numerator and denominator of another object.
@@ -2253,19 +2250,26 @@ def _getAtPath(root: MeterSequence, path: tuple[int, ...]) -> MeterNode:
     return node
 
 
-def _replaceAtPath(root: MeterSequence, path: tuple[int, ...], newNode) -> MeterSequence:
+def _replaceAtPaths(
+    node: MeterNode,
+    replacements: dict[tuple[int, ...], MeterNode],
+    ancestors: set[tuple[int, ...]],
+    path: tuple[int, ...] = (),
+) -> MeterNode:
     '''
-    Return a new root MeterSequence with the node at `path` replaced by
-    `newNode`, rebuilding each ancestor functionally.
+    Return `node` with each node at a path in `replacements` replaced, rebuilding
+    only the sequences in `ancestors`, the paths above a replacement.
 
     AI-assisted (Claude).
     '''
-    idx = path[0]
-    if len(path) == 1:
-        return root.setIndex(idx, newNode)
-    child = t.cast('MeterSequence', root[idx])
-    newChild = _replaceAtPath(child, path[1:], newNode)
-    return root.setIndex(idx, newChild)
+    if path in replacements:
+        return replacements[path]
+    if path not in ancestors:
+        return node
+    sequence = t.cast('MeterSequence', node)
+    newPartition = [_replaceAtPaths(child, replacements, ancestors, path + (i,))
+                    for i, child in enumerate(sequence)]
+    return sequence._rebuild(newPartition)
 
 
 def _subdivideNestedByPaths(
@@ -2274,20 +2278,22 @@ def _subdivideNestedByPaths(
     divisions,
 ) -> tuple[MeterSequence, list[tuple[int, ...]]]:
     '''
-    Subdivide (equally) each node reached by a path in `paths`, rebuilding the
-    root functionally, and return the new root plus the list of paths to the
-    newly created child nodes.
+    Subdivide each node at `paths` equally.  No path may lie inside another.
+    Return the new root and the paths to the new child nodes.
 
     AI-assisted (Claude).
     '''
+    replacements: dict[tuple[int, ...], MeterNode] = {}
     newPaths: list[tuple[int, ...]] = []
     for p in paths:
         node = t.cast('MeterSequence', _getAtPath(root, p))
         newNode = node.subdividePartitionsEqual(divisions)
-        root = _replaceAtPath(root, p, newNode)
+        replacements[p] = newNode
         for j in range(len(newNode)):
             newPaths.append(p + (j,))
-    return root, newPaths
+    ancestors = {p[:k] for p in paths for k in range(len(p))}
+    newRoot = t.cast('MeterSequence', _replaceAtPaths(root, replacements, ancestors))
+    return newRoot, newPaths
 
 
 if __name__ == '__main__':