While CC and CV modes have their specific negative effects *) and one need to be careful, the OP asked specifically for charging in CC+CV mode, meaning, with a both CurrentLimit and a VoltageLimit. This is a different thing. It means watching both limits at the same time. This means that such a charger would reduce voltage or reduce current as the other value approaches the limit. This means, never exceeding the current limit, and never exceeding the voltage limit.
If voltage is measured properly at the cell **), there is no way the cell can reach overvoltage condition of >4.2V, even if trickle-charge is allowed near the end for a prolonged time.
If the battery is designed to be charged up to 4.2V, then trickle-charging it with diminishing current up to 4.0V means that the battery will be kept in an under-charged state.
https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries charging up to 4.0V instead of 4.2V means storing 70-80% of the maximum charge a li-ion could hold if charged to its maximum.
Further trickle (i.e. 0.05C) charging (with cut off condition of 4.0V) would not hurt the battery, if voltage is not allowed to exceed 4.0V, because if it would hurt the battery, than it would mean that, by design, the battery is either not allowed to be charged above 4.0V, or is not allowed to be charged with charging current lower than some value, or both, and we precisely know both those sentences are false: max V is 4.2 and those batteries only have max-charging-current and no min-charging-current.
Be sure to also read "Overcharging Lithium-ion" & "Charging Non-cobalt-blended Li-ion" paragraphs from the above-mentioned article. Especially "non-cobalt" batteries mentioning li-ions with lower target voltage rating.
You may also find Charging li-ion cell using constant-voltage only helpful.
**) All traces, wires, connectors, etc have resitance. If you measure the voltage not directly at the cell, your measurement may read "4.19V" while it's "4.22V" few wires further at the battery. Be sure what exactly are you measuring and with what uncertainties.
- Using only CV, especially with a low-resistance charger output/cables/etc, may cause an excessive current to flow when battery's own voltage is much lower than the CV limit. This in turn may exceed battery's advised/safe charging current, may cause the battery to heat up, and cause all sorts of futher problems.
- Using only CC, once the battery reaches its max-voltage, CC won't stop, and will continue charging. Obviously this will eventually cause the battery to overcharge and its voltage to rise over the max-voltage. This may cause the battery to heat up, and cause all sorts of futher problems.
However, keep in mind that in both cases, "may" means it doesn't need to happen. Every voltage source has some finite max output current capability, every current source has some finite max voltage capability. If your CV voltage source has low max current output, trying to draw more than it can supply will simply overload the voltage source in some way and causing it to drop out of the CV mode and provide voltage lower than set. And similar for CC current source.
Of course if those sources are not designed for working in such conditions, it may damage them to some extent, but not the battery.
Of course a damaged voltage/current source may start misbehaving and may in turn damage the battery.
Of course you're doing it at your own risk. I did not advise you to do this.
I had to write this warnings in case some evil lawyers are reading this :)