Hi Steven - glad you're digging the lesson!

I recommend continuing to work on the double stops to get them down. Always make sure you are practicing the licks very slowly and correctly, and once you've found a nice slow tempo to execute the licks correctly, it's all about repetition - repetition - repetition at the slow tempo. This will loosen up your fingers and train your muscle memory to make it easier and easier to play the solo.

That said - if you find it difficult to play the double stops cleanly, and, for example, you need to perform the solo in front of an audience, then of course you can make adjustments and play the solo however you are able based on your current skill level. There's nothing wrong with that! Guitarists that cover other songs rarely play them note for note, adding in their own nuances and playing what comes naturally to them.

Also, the downstrokes in the solo are an expressive choice -- they add to the aggressiveness and high energy approach of the solo -- but of course, this is open to interpretation, and you can use alternate picking wherever you'd like!

Hope this helps, let me know how it goes!

Mike