You need a plugin Yanfly's Buff States Core.
Install it and in your custom state's field type:
Code:
<Custom Apply Effect>
$gameVariables.setValue(id, $gameVariables.value(id) + 1);
</Custom Apply Effect>
<Custom Remove Effect>
$gameVariables.setValue(id, $gameVariables.value(id) - 1);
</Custom Remove Effect>
Edit: in place of ID type a number representing your variable you wish to alter
I have tried this already and it did not work.
This is what I have written in the state's note box:
<Custom Apply Effect>
$gameVariables.setValue(4, $gameVariables.value(4) + 5);
$gameVariables.setValue(5, $gameVariables.value(5) + 10);
</Custom Apply Effect>
<Custom Remove Effect>
$gameVariables.setValue(4, $gameVariables.value(4) - 5);
$gameVariables.setValue(5, $gameVariables.value(5) - 10);
</Custom Remove Effect>
I don't think Yanfly's plugin will work here either because my game doesn't actually enter combat or maybe theres an incompatibility with another plugin.