Not possible to set an individual player's speed without changing their datablock.
There'd be a bunch of datablocks put in for different play-
waiiiiit a second.
Every playertype you add, make a copy in the setspeed addon and it'll put that datablock with different speeds?
Wouldn't be too hard to configure, you'd just have to put a file in the setplayerspeed.zip file and it'll auto dupe it to make different speeds for it (wouldn't pop up in datablockchange)
I'm not sure if that'll make sense, so if it doesn't just let me know