[Solved]Dynamic Conference:Block pin change after first user

I’m running Asterisk 1.8.11 . It seems I misunderstood my first assigment and did it correctly.So I apoligise for misleading some if they remember the old post. But now I have a question. I’ve set up a dynamic conference when the first user calls number 500 he is prompt to give two three digit numbers first is room number and second is pin and then he is automatically joined into that conference. And here is my question.

As it is now every next user can put the same room number but another pin and he will join that conference and changed its pin number. Can I block the pin change after the first user joins?

Did it by myself. If anyone is interested I can post my way to do it if not Please delete this topic.