I've been trying to find a wallpaper changer mod that will do the following, but can't find any.

Here's what I need it to do:
1) Load correctly (some of them don't)
2) Allow me to set a single command in a .rc file that will set the wallpaper to the file noted
3) Will support all image formats Windows supports for wallpapers
4) Allow me to include in that command a setting for style (stretch, tile, center)
5) Will execute that command on load and recycle
6) If it makes a difference in load time, if that wallpaper is already set, will ingore a command to set that wallpaper (if style is different, will only change style)
7) Allow me to set a command in a .rc file that will unload the module

I have found modules that make lists of images and change randomly, and plenty that work for bitmaps only. If a mod like this already exists, please let me know and also include the code to get it to do this because I've tried all the ones I found, and the code just doesn't seem to allow for something like this. Anything else you throw in is fine, I just need those things. Thanks.

on number 3, it needs to include, specifically, JPG support.

hrm. those are tricky :)
I use a script along with lswchanger for different preferences.
The wallpapers I get (not often) I often tweak and convert to .bmp anyway...

One thing I noticed with lswchanger (my preferred wallpaper module even though it's the only one I admittedly tried) is that, along with PNG support not working, JPG support only works if you (under LS 0.24.7) set the step.rc boolean LSUseSystemDDE to be true.

So with a smattering of scripting I think it's possibly to cover #1,#2,#4,#5,#6,#7. Since my using LiteStep for so long, I don't remember what extensions explorer supports.. What are they?
As for #3, using lswchanger w/ LSUseSystemDDE, you can only have .bmp/.jpg support.

The ending syntax you want might be a tradeoff though, because of this roundabout method with scripting...

But still, using scripting you can't really do #6 unless you read from the registry the keys My Computer\HKEY_CURRENT_USER\Control Panel\Desktop>Wallpaper, WallpaperStyle
...

Well, I just turned my wallpaper to PNG format and decided to use lsplus. It was a slight workaround - I had to get it to make its own list of wallpapers (wallz.rc) and cut the code for the bang command out of there, then I was able to do what I wanted with a script, rather than the other method which was extra rc files.

Still, I am wondering, is it possible to code a bang command that runs from a .rc file? For example, execute the bang command on LS load.

Use literunner or mzscript (literunner is more indirect; you specify a known window class that will load with litestep, like xLabel if you load that module).