The acrylic overlay provides some protection from ESD. The thicker the overlay the higher the voltage needed to 'arc' through the acrylic. If an ESD arc occurs, the acrylic acts as a 'resistor' to limit the current going into the capsense input.
Cypress should have a design Application note to cover recommended layout and ESD protection measures.
You theoretically can add transient-suppression silicon devices on your inputs such as transorbs. Hopefully there is a section on this in the Cypress App note. The potential issue with any silicon devices attached to the input is that the input capacitance will be increased. At best, you will have to adjust the tuning settings to accommodate this extra capacitance.
Thank you so much to All