If the tools have no electronics in them, just brushed motors, you can run them at whatever voltage you like, up to the point the mechanical stuff breaks. 20v to 24v is about 20% increase in speed, so probably ok for most things.
Really high voltage increases could break stuff:
Brushed motors have commutators that can disintegrate (grenade) from overspeed, but it takes a fair bit over normal speeds to do this. Some are marked with an RPM limit, many are not.
Gearing (in drills, etc) may be plastic and not handle really high speeds, or the torque increase that happens from all this. (I broke the clutch in a Ryobi hand drill even though the voltage wasn't really much higher, but it allowed enough higher torque it couldn't take it).
Grinders / disc cutters might spin the media too fast and cause them to explode; circular saws too.
But as long as the voltage increase is minimal, and no electronics are involved, it's unlikely to cause failures.
If there are electronics, such as speed controllers or brushless motor controllers, then those have to be able to handle the higher voltage *and* the turn on/off spikes that happen from the motors, and/or their sometimes wildly changing speeds under load during use. Some of these just can't take it.