You can set global blog permissions. Global blogs are those that are not associated with a specific space, group, or project.
Fastpath:Admin Console > Permissions > Blog
Permissions
On the permissions page, under Groups with access, assign permissions to user groups:
To assign permissions to a user group not yet added:
Click Add group.
Enter the name of the user group to add.
Click the Select Permissions button.
In the dialog box, select the permissions you want to apply for
the user group.
To edit permissions for a user group already added:
Locate the group in the list.
Next to its name, click edit permissions.
In the dialog box, select the permissions you want to apply for
the user group.
Click the Set Permissions button.
Creating User Overrides for Blogs
Create a user override to grant a particular set of permissions to an individual. You might need to create an override if:
A person requires a particular set of permissions for a place, but isn't
(and shouldn't be) a member of a permissions user group to which you've already assigned
permissions for the place.
A person is a member of a permissions user group to which you've assigned permissions for a
place, but the person requires a different set of permissions than those received
as a member of the place -- in other words, the person is an exception to the
rule. For example, you might want to separately define the person's permissions to enhance or limit their access in the place.
Use the following steps to create a user override on the permissions page you're editing:
Under User Overrides, click Create a user override.
In the box, start typing the name of the user for whom you want to set the
override. Click the user's name when you see it show up.
Click the Set override button to view the permissions you can
set.
In the permissions dialog for the person you selected, select and clear check
boxes as needed. In the end you want the list of checked items to reflect
the permissions the person should have. Note that you merely clear a check
box to remove a permission -- there's no need to explicitly revoke the
permission.
Click Set Permissions to save the override you've created.