I was not certain if this were specific to one Request or not, but having tried it now successfully with a couple of Request Items, it evidently should work any time you wish to steal an Item that is not a 'Present'. In other words, if the Item can be shipped, the 'cheat' will work. If the Item cannot be shipped (like the Strange Pendant and the Dragon Bones), it will not work.
The procedure is as follows:
1. Accept a Request to deliver an Item. An example of this is Hazel's Town Helper 1 Request, asking you to deliver Relax Tealeaves to Marjorie. Speak to the person who is making the Request and collect the Item, then ship it.
2. Now, go to the location where the Request was posted and cancel the Request. You will not be able to accept the Request again until the next day, but it should be posted at the same location the next morning.
3. Accept the Request and speak to the person who wishes for the delivery to be made. He/she should give the Item(s) to you again as though you never had received it/them before!
This worked with Sakuya and her Request to deliver a Tomato and Heavy Spice to Marjorie and Blaise respectively and the Relax Tealeaves Request.
Why did I bother to steal the items? Mainly because I was logging them for my Guides and it is easier when the data is displayed in the Shipping Container, but... it can be useful if the Item is rare or valuable!
Welcome to my Rune Factory 3 Site
Although HarvestMoonForever remains my primary site, you will find all my posts and Guides for Rune Factory 3 on this site. I created a site for Grand Bazaar in this manner and it has proven quite useful. The actual Guides as always will be published by IGN as well.