Proteins have a half life of ~24 hours. CJD has an incubation period of roughly 10 years. If de novo PrP synthesis was somehow halted, the likelihood of developing CJD would drop to zero.
On the other hand whatever job PrP was doing will also cease getting done, and its downstream pathways will be disrupted. So there are likely consequences.
Now if you could totally shut down PrP synthesis for like a week, then turn it back on, that might work. In theory this is possible using a tet-expression system [1], but I've never worked with a tet system that wasn't leaky. The only sure way would be to KO PrP genes from all cells, then CRISPR it back in a week later. Oh, and I'm talking about cells in a culture dish; this strategy would never work in an adult human.
[1] https://www.jax.org/news-and-insights/2015/april/introductio...