Is there anyway to a user with permission to start a workflow on all existing in a library over again? I mean not only when new item is created or changed, but in my case it's sometimes needed just to start the standard Approval workflow attached to a document library so that all of the existing documents gets approved again.
Thanks in advance.
I do not believe there is a "standard" solution for this. But, it also depends on your definition of "standard."
The only non-code way to do something like this that I know of is to use a complex set of Sharepoint Designer workflows to create a loop that will go through and initiate the workflow on all Items. See the reference for loops in SPD here.
A better way would be to use the SPServices plugin to retreive all the items in the list using getListItems and then starting the desired workflow using StartWorkflow.
Another Theoretical way would be to require content approval on the particular library and use manage site content and structure or SPD to mass check-out and check-in all the documents thus starting the content approval workflow.
