Just an fyi, 1 kHz battery impedance meter is not the best indicator of ionic migration resistance, which is primarily what electrolyte decomposition effects.
Mostly what you are measuring with a 1 kHz impedance meter measurement is conductive resistance of cell (mostly metal interconnects). The most prevalent damage item the 1 kHz impedance meter will show up is increased resistance due to electrode material delamination from the copper foil current collector on the negative graphite anode side and LFP cathode material from the aluminum foil current collector on the positive electrode side.
A little bit of bloating is not a disaster. Cells bloat during manufacturing charge forming process, but you typically do not see it because the manufacturer puts the pressure release port in after charge forming so the gas is allowed to escape before the cell is finally sealed up.
The visual gas bloating is not the really damaging part of electrolyte decomposition. The bad part of electrolyte decomposition is the hydro-carbon tars that are also biproducts of the electrolyte decomposition. These tars gum up the internal cell electrode material pores reducing the paths for lithium-ion migration. This results in a higher overpotential voltage (terminal voltage slump during discharge and terminal voltage bump during charging) necessary to get the lithium ions to move through the cells at a rate necessary to support the external demanded terminal current on the cell.
When you dissect a cell that has been severely overcharged with extreme bloating, when you unwrap the layers you will see the material which should be a uniformly flat black graphite colored electrode with a brownish haze color over it that is the hydro-carbon tar coating the electrode.
The cell wrap does not actually bloat. The top of the cell wraps are open to allow foil conductors to escape so gas just leaks out the top of the wrap laminates into the sealed outer metal container of cell. All you see is the bloated outside container. Usually, the bloating gas will eventually diffuse out through plastic terminal grommets in the metal casing. It may take a few weeks to a few months to totally deflate. You never want a burst pressure port however. That will allow electrolyte to eventually evaporate from cell.