Normally, we would recommend using our version of the GA tracking code documented here:
When you use E-junkie Cart buttons together with our version of the GA tracking code, we can add cart-button click tracking to the regular Analytics page-traffic monitoring, and we also take care of context transfer and ensure that we don't report duplicate conversions if the buyer returns to their thank-you page again. When you are using our version of the GA tracking code in your site, the thank-you/download pages we generate for you will automatically include GA tracking code with Ecommerce Tracking details whenever we detect a tracking cookie was set in the buyer's browser by our version of the GA code -- in this case, you should NOT add any GA tracking code to your E-junkie thank-you page customization fields, as that would conflict with the GA code we'd place in there automatically.
That said, our version of the GA tracking code only does what it does; as far as we know, it cannot be adapted to perform other GA functions that it doesn't already do. You are free to use the standard GA tracking code provided by Google for whatever tracking needs you wish, instead of using our version of the GA code at all; doing so would give up your ability to track cart button clicks and give up the Ecommerce Tracking details we place in your thank-you pages for GA to pick up, but it would give you the freedom to implement whatever other GA tracking features you wish.
Regardless of whether you use our version of the GA code or the standard code from Google, make sure you only use one version or the other everywhere you want to use GA tracking -- i.e., do not mix-match our GA code and Google's code on the same page or across different pages of the same site.
It sounds like the tips on this help page, in particular the section "If you are selling only downloads", may also be relevant to your needs: