<T6> states (emphasis mine):
Fields may be repaired at the Event Partner’s discretion. All competition Fields at an event must be set up in accordance with the specifications in Appendix A and/or other applicable Sections. Minor aesthetic customizations or repairs are permitted, provided that they do not impact gameplay (see <T4>).
An example of a permissible modification to the Field listed in the rule is:
Using non-VEX electrical tape to add required lines to the Field
Would substituing the red and blue tape lines that define the Load Zones with white tape lines be a permissible modification to the Field?