Hi readytohittheroad,
Lots of us do some or all of the work on our own, and in many cases, Heartland will send you parts to do so.
Be aware that your appliances and some subsystems are actually warranted by the supplier. Normally if you go to a dealer for service, you don't get involved in the details. But when you become the servicer, you have to deal with the same things your dealer does.
Some suppliers will probably not want you doing your own work and probably won't send you parts under warranty. In my experience, Dometic is one.
If you cause damage while attempting a repair, I'd expect that most suppliers would not pay to repair the damage you caused.
To your specific question about voiding warranties, I don't think that's an issue.