Newbie question: How to change limit values to custom attributes?

Hi all!

I'm a student in 3D Animation and I'm new to the forum and to MAXScript itself.

I'm currently animating a custom rig and I want to modify the limit values of a Custom Attribute created using MAXScript. I know the attribute was scripted to the Attribute Holder because when I open the Parameter Editor (in 3ds Max 2008) it doesn't show the parameters.

How can I access and modify the limit values of this kind of custom attribute?

Thanks in advance, and any help will be more than welcome!