Question:

How do you tell schools to not look at your file until you appear for the Jan 2020 LSAT i.e. ignore your scores so far ?

Seems like CAS will report every score after it is available but the school might not know you registered for a future LSAT and might give a decision without considering your future LSAT score.

Link:

https://www.lsac.org/applying-law-school/jd-application-process/credential-assembly-service-cas/law-school-reports

https://www.lsac.org/lsat/taking-lsat/lsat-scoring