How to use when-checkbox-changed event in personalization or custom.pll

Hi!

My requirement is user should not allow to uncheck the check box of apply in Receivables Receipt Application window on basis of some conditions, I have tried using when new item instance but it is not working fine after un checking my event is firing but I have to restrict at the time of click not after that.

Any suggestion on this and tell me if I can use when check box change event in custom.pll as this is not available in personalization.

Thanks in Advance