can the students use non offical vex IQ parts like R8 e. from the V5 rule book be used? (An unlimited amount of rope / string, no thicker than 1/4” (6.35mm)).
As noted in your question, the VIQC Legal Parts Appendix provides a comprehensive list of legal VEX IQ parts. Furthermore, rule R8 (quoted below) lists all legal non-VEX IQ components. Rope/string is not included in this list; therefore, it is not legal.
<R8> Non-VEX IQ components. Robots are allowed to use the following additional “non-VEX IQ” components:
a. Appropriate non-functional decorations, provided that these do not affect the Robot performance in any significant way or affect the outcome of the Match. These decorations must be in the spirit of the event. Inspectors will have the final say in what is considered “nonfunctional” and “appropriate”.
i. Any decorations must be backed by legal materials that provide the same functionality, (For example, if your Robot has a giant decal that prevents Balls from falling out of the Robot, the decal must be backed by VEX IQ material that also prevents the Balls from falling out).
ii. The use of non-toxic paint is considered a legal non-functional decoration. However, any paint being used as an adhesive or to impact how tightly parts fit together would be classified as functional.
b. Rubber bands that are identical in length and thickness to those included in the VEX IQ product line (#32 & #64).
c. ⅛” metal shafts from the VEX V5 product line.