Hey Fruitrocket, this may help.
A while ago a chap called Ninjafada from the SweetFX thread on Guru3D made a simple DX9 image viewer. I hope he doesn't mind me sharing it here.
Download: DX9IV (DX9 Image Viewer) 1.4
To use:
Extract Reshade to the same dir as DX9IV.exe. Rename the .dll to d3d9.dll
Take a screenshot of your game
Drag the screenshot onto DX9IV.exe
As a DX9 viewer it hooks Reshade (or back then, SweetFX) as it loads, and displays the screenshot. You can then edit the shader configs and reload the shaders, or with Reshade I expect it will update by itself. Much quicker to play with shader settings and see the effects without the need to load a game.
However it's *very basic*. It runs full screen only. There are no key controls except Alt-F4 to quit. All it's doing is displaying an image through DX9. But it's still faster and easier than experimenting while a game is loaded.
Ninjafada made it as a stop-gap solution about two years ago. In fact I haven't even tried it with reshade, forgot about it until I read this thread, might do that now.
EDIT: Found Ninjafada's original archive, updated link above.
EDIT2: And yes, just tested and it works with Reshade

Image updates just 1 second after a changing an ini file. I completely forgot about this tool, thanks for the reminder! With the new Framework and all the new shaders I have no idea how most of them look, I'm off to see how different lens flare effects work with some games
EDIT3: After having a quick play, recommend setting the following in the Global settings when tweaking, as being a still image these will otherwise remain on screen:
#define ReShade_ShowToggleMessage 0
#define SweetFX_Greeting 0