It should not touch the contact_id at all if the only fields mapped are, for example id and package as in this example. This is with the contact options left as default on the import screen (shouldn't matter).
Also fix the 1185 contributions incorrectly changed to contact_id 72.
Change #1248945 had a related patch set uploaded (by Lars SG; author: Lars SG):
[wikimedia/fundraising/crm@master] De-anonymize contributions borked by contribution import
Change #1248948 had a related patch set uploaded (by Lars SG; author: Lars SG):
[wikimedia/fundraising/crm@master] Don't anonymize contributions if imported by contribution id to update
Change #1248945 merged by jenkins-bot:
[wikimedia/fundraising/crm@master] De-anonymize contributions borked by contribution import
Change #1248948 merged by Eileen:
[wikimedia/fundraising/crm@master] Don't anonymize contributions if imported by contribution id to update