First would be the option of software mouse option in the game, several software configurations can cause a hardware mouse pointer to be unfeasible within Xsyon.
Ideal? not but it should always be an option to avoid anyone being literally unable to play in fullscreen.
Secondly i would recommend that the Xsyon options files be saved in plain text format to allow for changing settings, or alternatively include a wipe options button in the launcher to allow the player to wipe his settings without having to navigate the files and delete manually, convenience option for sure but some players these days are really not all that computer literate and having an easy button for it will avoid reinstalls for some people.