how to change a CONSTANT defined in a class file?

[sugar]

Hi, I have the folowing php question:
I have 3 files:

the file a.php wich includes this php class: [ include "b.php"; ] (and more code...)
the file b.php wich includes this other php class: [ require_once("c.php"); ] (and other functions of course...)
and the file c.php wich has this definition: [ define('MAX_CUPS', 148); ] (and other definitions...)

My question is how can I overwrite the defined "MAX_CUPS" value for instance if I need sometimes 148, sometimes 400, sometimes 800, etc.
How cai I set this "MAX_CUPS" value again from the a.php file without having to edit the c.php file?
I read that "A constant's value cannot be changed after it is set", but im triying to get help with this issue...

Thanks indvance.

Aldo.