How to modify data from developer console

Hi,

I've just started using the Developer Console for publishing apps to my customers. for the previous projects i exported and imported the DS file to the customer account.

It's still not clear to me how to use the developer console correctly.

1 - Can i modify data on my customer live app after publishing it? when i "access application" i don't see the customer records,

2 - If the customer want the application code can he get it without my permission?

3 - Publishing to ZC5 and ZC6 accounts is the same?

My use case:

I developed zoho creator application for a customer and after finishing , few more customers contacted me for using this application.

I want to charge the customers yearly for the use of the app without to expose the source code.

Thanks in advance,

Naveh