How can I auto increment a uniq row index with a set prefix?

Hi Excel Forum'ers!

This is my first post so here goes...

I have a spreadsheet which i use as a sequential job task sheet. Each row has a unique job reference e.g. JOB01.
Each job reference may also have subtasks e.g. JOB01.01, JOB01.02 etc

Is there a clever way (without using VB - as Im not familiar with how to use it and put such a fix in place) to do the following automatically or using a shortcut key(s):

1. Each time I add a row under a job reference, it auto-populates the sub-task with the correct job reference. So if I create 5 rows under JOB01, it'll populate them with JOB01.01, JOB01.02, JOB01.03 ...JOB01.05 ?

2. Add or delete rows where the job reference number automatically adjusts to keep each job sequential

Thank you

Shabs