Open [Location of your World of Warcraft folder]/World of Warcraft/Intercace/Addons/Cursor/_Cursor.lua
You can edit it with any text editor you please. I prefer Notepad++, but the plain ol' Notepad that ships with Windows will work too.
The lines of interest are between 68 and 158. All the models _Cursor has are listed here, along with their scale factors and offsets.
One such line looks like this:
["Weather, cloudy"] = "spells\\goblin_weather_machine_cloudy|1.5|2.1|11|-9",
What you're interested in tinkering with are the last four numbers. They are listed in a specific order, separated by vertical bars. From left to right, they are: Scale factor, default rotation (should be safe to just leave alone), X offset, and Y offset. This particular model uses a scale factor of 1.5, a default rotation of 2.1 radians, an X offset of 11, and a Y offset of -9.
Some lines omit some of these values. A couple examples:
["Sparks, periodic healing"] = "spells\\lifebloom_state|||8|-8", ["Sparks, red"] = "spells\\immolationtrap_recursive|4",
The first line here is missing a scale factor and a rotation, as denoted by no number where one should be. It has a scale factor of 1, rotation of 0, X offset of 8, and Y offset of -8. The second line is missing a rotation and offsets, as denoted by simply ending early. It has a scale factor of 4, rotation 0, X offset 0, and Y offset 0.
If the scale factor is missing, it defaults to 1. If rotation, X offset, or Y offset are missing, they default to 0.
To actually test your tweaks, you'll need to save your new _Cursor.lua, then open WoW. If WoW is already open, you can type /reload to load the most-recently-saved file.