To our best understanding at this time the cancer formation is secondary to chronic inflammation. In cats, and we think in dogs, is from the adjuvants. We do not know if one adjuvanted vaccine is worse than another in dogs. Rabies is provided only as a killed vaccine and as such is always adjuvanted. To my knowledge the only non-adjuvanted rabies vaccine available is the feline rabies by Merial.
As far as switching sites while this may have some benefit, if the inflammation resolves within 2 weeks, then re-administering a rabies vaccine in the exact same location three years later should have no impact. I think the problem is the chronic inflammation. If there is a low grade persistent inflammation at a site for months to years, then the risk of cancer is present. I use a smoking metaphor - if you smoke one cigarette, the inflammation and carcinogen exposure is gone fairly quickly. The risk of cancer comes from the daily exposure for years and years.
If you do want to have the vaccine administered in a different site, there is no change in efficacy. The site of injection on the pet for vaccines has absolutely nothing to do with how the vaccine works.
Unfortunately there is NOT enough studies on this and it is difficult to obtain funding. Testing how a medication or vaccine works is easy to fund - the company that hopes to sell the medication or vaccine covers the costs. Testing that vaccines cause cancer which might entail a loss of profit for vaccine companies is NOT funded by the big drug companies.
Furthermore VAS is difficult to track. It can take months to years for VAS to form, often pets have been given different vaccines from different companies over the course of time that the VAS forms, etc...
, I wish I had better news for you...