Hi Rajesh,
Copying a role means that the standard remains untouched. This means an upgrade will be easier as this element does not needs to be reviewed for merging. Moreover you will have a working example if you need to review other things.
It is possible to have a naming convention where you e.g. include your Company name in the description of your role.
Privileges related to posting of journal all start with the technical name: LedgerJournalPost. You can find out which roles/duties are using them. Probably you also need to duplicate the standard duties which allows entry and posting of journals. Then in the duplicated duty, remove the privilege which provides the option to post. Attach this duty to your new role.
You can also do this using the Security Development Tool. I explained it in this blog: kaya-consulting.com/tips-on-ax-2012-security-development-tool-part-2