So I created a separate plugin just for maintaining already existing pages. This way I can give them independent admin access without the ability to create new pages or change the important stuff to break site (f.e. SEF-URLs that are used for page scrolling)

Then I found that it is easier for me too to maintained pages on some other site, and I added some preferences to be able to use this plugin without original limitations.

So what does this plugin do:

• by default, it displays the page table records (no default limitation) 
• by default, it displays only fields: menu_image, page_title, page_text, page_author, page_order
• by default, it displays only edit and order options

Options:

• disable any available field for editing
• display only pages (so only records with page title filled are displayed) 
• hide help information 
• display delete button 
• limited display to authors (logged admin sees only their pages). Exception for main admin. Author field edit should be set off then.
•  disable order button (by order field edit off) 

You can download this plugin from this site.