I'm trying to set a site up so all the pages inherit permissions from the page defaults.

Basically I want to restrict a user group from editing a few blocks such as the nav etc.
The pages are set to inherit permission from the page defaults. However when I change the permissions of a block on the page defaults, they do not get passed down. The only way I have managed to get this to work is by deleting a block in page defaults for a page type so it is then deleted from all pages using that page type. Then adding the block again, setting permissions then adding the block back to all the pages using 'set up on child pages'.

I hope the above makes sense, any help is greatly appreciated.
I just want to know if there is a 'real' way to do this that is quicker.