You can create a generic ID, certainly. But that ID will still need to have access to the various databases. You can start the process by launching the Notes client on the server machine (after taking the server down) — if you’re using a Windows box, launch the nlnotes.exe app. You will then have effectively unrestricted (Manager) access to all databases on the server and can change ACLs at will.
I wouldn’t suggest using any single user, even your “admin” id, directly in the ACL — at least not by itself. Instead, create an admin Group in the public address book and add that group to the ACLs.
Unfortunately, there is no tool in R5 to allow you to play with ACLs en masse when running the local Notes client (nlnotes). If you were on Domino 6 or higher, all you’d need to do is modify the Domino Directory to give yourself sufficient access to the directory, then grant yourself Full Access Administration privileges on the server, then you could use the modify ACLs tool in Administrator to fix ’em all at one shot.