Can't.
The server assume you spent all 3 points, so if it is capable to continue with some points left, the server and client total stat will not match, and cause disconnection after the skill screen.
It is better make suggestion to the developer to allow not spending all point.

Bump

ok?

for my fighter i use cheat engine make my magic negative then i can increase other stat
now my stat look like

Str 25xxx
agi 25xxx
will 25xxx
magic -100xxx
con 25xxx

but my cheat char cant change equipment anymore
 

I'm currently working on hacking this game. Battles seem to take place on local, so there is a chance you can influence the game, like high damage, infinite hp/stamina, insta win.
Dont get your hopes up tho

Edit: Yep I just necroed, but idc, I'm still gonna give it a try, games cannot stay unhacked forever.