Hi Tim,
I have noticed that sometimes meditators go to the Goenka courses just because it is free and take undue advantage of it by breaking rules set for the meditators own benefit and continuing to do practices that they feel are superior to what is taught.
Having been a practitioner in this tradition for almost 2 years, my sincerest advice to you is to follow the rules with complete honesty, to your fullest ability. When you join, you are asked to keep all your other practices aside for 10 days to give this technique a fair trial and after the course you're free to do as you wish.
Based on the experience of thousands of students, it has been observed that people who continue to follow their own practice or rituals inside the dhamma center end up in a huge mess. They sometimes cause immeasurable harm to themselves and it becomes extremely hard for the assistant teachers to spot or rectify the subtle problems that consequently develop. This is also not conductive to others who are meditating along.
This technique of Vipassana is so deep and so subtle that you cannot really understand it other than by sincere practice. It's like a deep surgery of your mind and at several points in the 10 day course you might have huge mental resistance that will urge you to the opposite of whatever needs to be done. At such times, ignore these urges and keep following the instructions.
Please understand that the organization only wants to help you grow in Dharma, and these rules are set for your own benefit. They have literally nothing to gain by holding you back or making rules that are not really needed.
Helpful read:
http://www.vridhamma.org/Question-and-Answers
Can we combine two or more meditation techniques ?
You can combine as many techniques as you like, but don't combine them with Vipassana. Vipassana is unique technique, and combining it with anything else will not help you. It may even harm you. Keep Vipassana pure. Other techniques only give a veneer to the surface of the mind. But Vipassana makes a deep surgical operation; it takes out complexes from the depth of the mind. If you combine it with any other technique, you are playing a game which may be very harmful to you.