See, I have given you the caution for opening the period in advance..
The Posting Period is head of MM module. And you want to play with this.
I will never give the suggestion.. If you can't able to do anything for the material in period June, then you have to wait till 30th June.
If you really want to open July period, then My suggestion is please consult your your organization manager and your other MM/SD/PP consultants.
If they will approve it, then you can do your process. But never do it without written permission.