F5 ASM Filter/Block Parameter without blocking page

An example what I think to do is, I have the path from input fields, there are just numbers allowed. If the user put now some symboles into the input field the ASM would block it, but maybe is it possible to clear the fields fill it with just zeros (00000000) and the application give us back that this entries are not valid and so I can maintain my session and I do not lost some data from the input fields or text boxes ! I hope to get some best practices for this case or how would be implement this regular because I think I'm not only the ONE who want to do this ;)