Are the effects of computer eye strain temporary?

Yes. Our eyes are designed to see things in 3d. When you look at a computer/book etc for a long time (a 2d surface) you can strain your eyes or get dry eyes. Every 20 minutes rest your eyes for 20 seconds by looking at something at least 20 feet away.
Yes. Resting your eyes will help. Refractive error changes such as myopia and presbyopia may not reverse until the eye grows or a cataract forms or is surgically corrected.