Unique field value

I am not a nerd, I cannot write the code myself. I note that the system can verify e-mail-addresses for existence and will ensure unique userids. However I have an integer member number field that must contain unique values. Cannot use the system ID number, because my member numbers do exist and are already in use in external financial systems.

So what do I have to ask someone for, to have them make the code for a numerical uniqueness field check?

My own crazy idea "heaven" is as follows: Would it - at the SQL level - be possible to unload the Joomla CB user table, reset each index value (ID) to be identical to my own member number, and then reload the table?

The fact is I do not care what number NEW ones get - they just have to be unique, and the old ones have to be preserved. In my case nex ID is 1015, and highest current member number is 898. So letting IDs from 1016 up be used as member numbers for new ones is both acceptable and preferable.

Only I do not want neither Joomla nor CB to blow up.

Oh yes, and I need to be able to show that number as a protected field in a Tag...

That'd be cool, i need the info too... How to make an unique field? Like an ID number for each user.

I'll be expecting any helpful answers you can provide, Thanks a lot!