It should work with any attribute. The actual item that I used to test this out, and that Paul helped me with was for Intelligence. When I was testing $MyIndex (instead of $TargetIndex) I did it for Dexterity.
For Charisma it should read:
Code:
$SET_CHAR_ASL($MyIndex(),"Char25",25-#$GET_CHAR_CHA($MyIndex()));
$SET_CHAR_CHA($MyIndex(),25);
And
Code:
$SET_CHAR_CHA($MyIndex(),$GET_CHAR_CHA($MyIndex())-#$GET_CHAR_ASL($MyIndex(),"Char25"));
(For the Activation and Deactivation scripts respectively.)