Duplicate user IDs causing issues

My old site, which sold digital content, went down a few weeks ago, and I’ve since rebuilt. I’ve tried importing the old user tables (because users have lifetime access to their content), but now for each new user, the user ID is shared with a user from the old database, resulting in both users’ content being accessible.

Since i only have a dozen new users with conflicting IDs, is it possible to start new user IDs at the number 500 and add incrementally? I have apporximately 490 old customers.

Thanks.