I noticed for the dos games you included a handy output switcher utlity for those who do not want to mess around with the dosbox.conf. Could you also add an option to run the game's original setup program?
I noticed with say - Redneck Rampage - it's set on a specific resolution using specific controls. If I want to change this I have to mount the folder myself and run the setup. While thats not a huge deal, it would be a little more convenient to have a "setup" button which launches dosbox + the games setup.exe program.
Most people probably wouldn't use it, but it would be nice to have.

Not sure but I think you can do it yourself by making either a shortcut or a batch file.

Oh I know I can do it myself, but I imagine the less technically inclined folks might not be able to. Most dosbox front ends, for instance, include the ability to add the setup as a shortcut.

I'd like to add one thing to that. I know from the documentation that you're supposed to be able to make the DOSBox window scale by editing a few specific lines in the dosbox.conf file...but I've had exactly 0 luck trying this on my own. It would be great if that little "select rendering device" dialog in the GOG launcher included (if the rendering device supports it in DOSBox) a "Windowed" checkbox and a "windowed resolution" dropdown.

from what i can tell, the setup for redneck rampage is the original game setup.

I made a suggestion on day one to have a front end to DOSBox involved in the download, as they are so easy compared to using the DOS type commands in DOSBox. You could say DOSBox is DOS and the front-ends like D.O.G and D-Fend Reloaded (available on the DOSBox site) are like Windows 98, a sort of DOS front end.
I complain on lots of sites that when an old DOS game is mentioned all the hardcore gamers go on about how to set up DOSBox with all those convoluted commands. No one ever mentions a front-end, and 2 time out of 3 the person comes back 2 or 3 times with further questions. What you end up with is a thread not talking about the game, but talking about DOSBox configurations!
I have always used a front-end for my DOSBox games, even though I could use the DOSBox commands. This is because of all the features front-ends offer, like easy trial and error to get the best running game with just a couple of mouse clicks and game starts/closures. Also they allow multiple versions of DOSBox, they give space to make your comments on the game and they allow you to score the game and put in the release date, genre, etc, then being able to bring up in your list just a particular genre, scored or date of games!

Front-Ends can be found here: http://www.dosbox.com/download.php?main=1
Personally, I like D-Fend (Though I see it is no longer around and my copy would be very out of date).
Not all front-ends are available under a permissive (?FOSS?) license, so I guess the best way would be to give a list of possible options, rather restrict people to a chosen one.

D-Fend has been taken over by another programmer - hence it being now being called 'D-Fend Reloaded', which is now available on the DOSBox site instead.

... It's already in Redneck Rampage. In your GoG's All Program folder.