All files used to define and list a solitaire version in SoliLuxe can be found in the /rules folder (except for the solitaire quickbutton icon, which is placed in the /images folder).
To examine or tweak the rules for an existing game, it is sufficient to open (and possibly edit) the corresponding [game name].xml file in the /rules folder. Just remember that the files delivered with the game will be overwritten if you update the game to a new version, so for permanent changes you must copy and rename the altered files. NOTE: It is essential that you also change the name="" attribute in the new file's <patience...> tag, since this name must be unique for each rule file!
To learn more about adding solitaire versions and new games, please study the PDF Patience Definition Guide in the /manuals folder.