There's no need to make modifications to the core, nor will we help you in doing so (we don't support core edits). This can be done with documentation subscriber incubator project CB Queries. This plugin allows execution of database queries (full substitution support!) at various triggers such as after user logs in. This would allow you to execute your query with absolutely NO php editing safely. More information on incubator projects can be found here .

I like their extensions as well, but their unwillingness to give up their source code even to members who paid for licenses is a dealbreaker.

All development except CBSubs is open source so you're free to edit them as you feel necessary. This means there is no encoding in place for CB Queries and various other projects. Notice that CB it self is not encoded.

If I can do everything I can ever possibly want to do without ever touching CB code, then I'll be a happy man. Are you telling me if I get CB Query and all the rest that there's no possible scenario in which I would need to touch the code? I would be hesitant to believe you if you said yes.

If all you're wanting to do is execute a database query say after a user logs in or after a user registers (or any other CB trigger.. see tutorials within my signature for trigger information) then yes you never have to touch CBs source code AND your queries would carry over everytime you upgrade CB, which would not happen if you made core edits.

We also need an extra user field called 'Member ID'. This integer field would be set when a user registers and would be an auto_increment database field. Anytime a user signs up, he/she gets assigned the next 'Member ID' integer, and the counter is incremented.

Users are already given a unique auto-incremented value. You can display this value using a delimiter field with the substitution [user_id].

Alternatively you could create a Read Only integer field. Then using CB Queries on the trigger "after registration" you can check and update that field to the next value. This would take a little bit of a complex UPDATE query then a simple + 1 appended to it (you should order by the integer field), but again completely doable without altering source or creating a new fieldtype plugin.

We also need to be able to create a small form on the backend that would reset the counter to whatever value they wanted.

Not sure how you'd achieve this aside from making the query explained above more complex.

Once again, I would love to become a subscriber, but I need to know that I can accomplish this custom solution before I can commit to becoming a habitual CB user.

There's no guarantee any of the plugins will provide what you want. Incubator projects are a bit more complex and "state of the art" as they're my personal projects with "no strings attached". There is no documentation for them and no official support for them (aside from the projects forums page).

Best I can suggest is review the incubator page given earlier and if at least 2 or 3 of the projects can be of user then it would certainly be a worthy investment IMO.