This command will give the invoking character a specified number of base and job
experience points. Can be used as a quest reward. Negative amounts of experience
were not tested but should work.

getexp 10000,5000;

You can also use the "set" command with the constants defined in 'db/const.txt':

// These 2 combined has the same effect as the above command
set BaseExp,BaseExp+10000;
set JobExp,JobExp+5000;

You can also reduce the ammount of experience points:

set BaseExp,BaseExp-10000;

Note that 'getexp' is now subject to the 'quest_exp_rate' config option, which
adjusts the gained value. If you want to bypass this, use the 'set' method.