False positive ASM block

Yep. Navigate to Application Security -> Parameters -> Parameters List and then select the policy you wish to edit. Create a new parameter, name it appropriately, and set it to a user-input value. Then at the bottom, click the attack signatures tab and select the signature that is incorrectly firing on the parameter and move it over to the overriden security policy settings pane. Ensure the dropdown for this signature says disabled.

This will disable the attack signature only for the specific parameter.