Animate textual changes in keynote
If I understand you correctly, you want the first bullet point to exit stage left, and have its replacement arrive from stage right. Then repeat wi point three. 

Create each bullet point in its own text box. You can manually mimic the build in to match the rest of your presentation. Once the slide's build is complete, the easiest animation might be with a couple of additional slides set to Magic Move. 


slide 1, original text in place; bullet 1 replacement off screen
slide 2, bullet 1 replacement in-line, original off screen, bullet 3 replacement off screen
slide 3, bullet 3 original off screen, mullet 3 replacement in-line


If you're familiar with the Magic Move transition, this should make sense. If you're not accustomed to it, play and discover some fun!