Homing and mesh probing are 2 separate actions, by setting
#define MULTIPLE_PROBING to 3, you inherently create 3 slow probing points for the mesh probing (not the homing probing), with 2 you get a fast/slow probing action.
Everything is possible, but, that means that you need to dig into the sources; not changing the configuration constants. That is not for the faint hearted.
I've seen the responses of fast and slow probing in action, usually the difference is not existent or very very small, like one or two hundredths of a millimeter, I seriously wonder if it makes sense to use more than 2 probing points.
Please note that a damaged bed may benefit more from increasing the probing array amount (from 3 x 3 to 4 x 4 / 5 x 5). The number of probing points discussed earlier only dictates the amount of probing actions in a single point; if the sensor hits the bed the probe measurement is done, if it hits again, the value should more or less be the same (give or take the accuracy of the sensor), I do not see what damage to a bed would imply more probing measurements in a single spot. The only rationale would be if the sensor itself has a large inaccuracy with an error that is not systematic, but random. My BLTouch (original) is pretty accurate and repeatable, I've had more issues with all those cheap knock-offs.