If you change settings after you pick a drawing tool (line, shape, etc), the settings sometimes revert to defaults when you change tool (changes apply only to that tool, usually only a single object). If you change your settings when the selection tool (arrow mouse pointer) is active, settings should stick (apply to all subsequent objects you draw).
To make your choices default settings for new objects, sticky also across save/open, you need to change the Default object style. The style is local to the file, so it will not apply to other (or new) drawings. This will also change appearance of drawing objects which have not been directly formatted.
You can make a drawing template and base your new drawings on that. This way you alter settings also for new drawings (by changing the template). Still it will not apply to existing drawings.
Apache OO 3.4.1/4.1.2/4.1.3, on Ms Windows 7/10 and Mac OS-X 10.8.5 and 10.11.
LibreOffice 18.104.22.168 on Mepis Antix MX 14