Unique record ID

I am new to Zoho Creator and have two questions.

First, I have a simple application and would like to add a unique record ID to each record in a form as it is created. I know I can use an "On Success" script to access Zoho's own ID, but that ID is too long. I know I could trim it down to five digits, but even that is too long, so I'd like to be able to create ny own unique record ID starting from 1, or whatever number I pick. Is there an easy way to do this?

My second question follows the first. Once I do set the code for the above, how can I retroactively create a new record ID for the 1400 records I currently have in the database, that were created before this code would have been written?

Thanks in advance for your help.