Figured this out -
To do this, I've set solr.in.sh as follows:
SOLR_HOME=/data/var/alfresco/solrhome
SOLR_SSL_KEY_STORE=/data/var/alfresco/solrhome/keystore/ssl-repo-client.keystore
SOLR_SSL_TRUST_STORE=/data/var/alfresco/solrhome/keystore/ssl-repo-client.truststore
With no other changes. I've also moved the existing solrhome directory
to the new location. Should this work?
This isn't sufficient to move solrhome. You also have to find the
solrcore.properties files in the existing/moved solrhome directory, and
edit any instances of solrhome in those files to show the new location.
This is enough to get everything running again.