First things first. The "adding a Group seems to only allow audio cues" was a glitch. I was using the drop down menu to add a group and it was at the top of the menu. After a reload it moved to the 10th item in the menu, the first being "Audio". So this is why trying to add a group was adding an audio cue. The same thing happened today. The menu was reordered and even "Command 0" still added an Audio cue and not a Group so it's not just a temporary order of the menu thing. It seems to be that once I add a cue it returns to the intended operation. ie. hitting "Command 0" twice in a row added an Audio cue first and then a Group cue. I'm sure this has been fixed in updates as I'm on 5.2.4 currently.
Back to the meat of the matter.
I have an acceptable result by creating a custom fade to automate the Gamma value. I saw an example someone had used to make flickering light to create a fire effect. When I had originally tried to loop a couple of very fast fades it caused playback issues and sometimes erratic behaviour of the the timeline; specifically, missed pause cues for that same effected video. With this new custom fade I simply added multiple up and down points creating a sawtooth. I needed 2 because 1 would leave the value in a place where repeating it would no longer cause any effect on the next pass. Fade out on effects parameters doesn't seem to be a thing (how to I do it without stopping???. Again, I'm pretty new so please don't attack my ignorance :) ) (Thanks member:micpool for adding that as the first response, in the middle of this book I'm writing. I've only been here a day but I understand you are a mighty contributor and I thank you for your help)
So, this worked great to produce the effect I wanted..... BUT..... I wanted the video to fade in from black with the effect fading in with it; like a projector lamp warming up, not like a shutter opening. Fading in the fade, also doesn't seem to be a thing. It would need to be applied as a relative thing and that doesn't seem to be a thing either. I'm not sure how to "math" that either but, I digress. So, the result would be that I couldn't fade in the effect of the flicker with the video fading in. Starting the flicker ahead of time, with the video opacity at zero, and then fading in the video would cause it to jump to full opacity during the fade and the effect would be way more dramatic until the opacity fade was complete, then the effect would look as intended. I never did find a way to sort this out. I was confused as the fade in was affecting opacity and the effect fade was affecting gamma.
Again, I went back to trying to find a stand alone LFO to work on the Gamma value via MIDI, or to write a script (huge learning curve for me, how does one incorporate timing into a script).
Then the same problem happened with the fade out. If I stopped the effect fade first, then the video fade would work as normal. If I tried to fade the video and the "flicker group" together, then the video would snap out. I wanted the video to fade out as if the flicker was baked in (it could not be because at this point, and various other points in the previous 5 minutes, the video was paused). There was a lot of complicated head scratching and then the simplest of solutions hit me. ... JUST COVER IT ALL WITH A BLACK PICTURE!
So, because this whole set of cues, involving this "flickering video", comes from black, I start the stack with a black picture placed on top of the video element. The video is started and paused, to the first freeze before any motion is temporarily needed, and the video flicker stack loop is started (just like micpool's example below), and then my first cue is now fading out the black cover picture instead of fading in the video. At the end I fade the black picture in over top of the video before stopping the flicker effect and video.
This produces the results needed and I didn't have to learn any scripting or install anything new or interesting on a client show laptop. It also saved me from putting a fan on a lighting dimmer in front of the projector lens :)
Now the whole video cue looks just like the archival footage that was sent to me. Too bad the only reason it looks like that wasn't a design choice but an artifact of the framerate difference between their projector and video camera. (the dang intermission slide flickers too)
I hope this has been a worthwhile addition to this group and I'm looking forward to digging around looking for other cool things to do with Qlab.