Personalise the right click function for what? Depending on where you "right-click", different actions can be performed. On a form or report, it opens a popup menu that you can specify using the ShortcutMenuBar property, on a control it does whatever you want provided that you have created the proper event handler (event OnMouseUp with testing of the Button parameter).
If it's for using in a textbox, you'll need to write a TextBoxName_OnMouseUp event handler. The code in it should test to see if the right button was pressed by checking the value of the Button parameter (the procedure will be called whichever button was pressed), then use a Windows API or perhaps a macro-style command (DoCmd.???) to paste the content of the clipboard into the textbox.