I want a close icon in the toolbar so I don’t have to keep closing and re-opening LO. I also want to be able to replace characters with special characters easily.
Please use a separate question for the second topic, but first search. You will likely find some answers. Solutions are possible with Find&Replace, with AutoCorrect or with keyboard layout.
You do not need a close icon in the toolbar. If there are more than one document open, the X in the title of the window will only close the active document, not the whole application. If only one document is open, you will get an additional x right, top in the menu bar. This x will close the document but leaves the application open, so that you get the StartCenter again.
If you nevertheless will use an icon in the toolbar, you can customize a toolbar. The needed command is .uno:CloseDoc. It is the same as item Close in the menu Format, where you can see, how the icon looks. You will find it in category Document
, command Close
in the Add part of the customize dialog.