Firstly, I want to thank user Ozymandias for their guide, this is more an addition to that one than anything else and I literally wouldn't have been able to get as far as I got without it.

1. Change the turning-while-shooting behavior so that, well, you can, and adjusting the shank action so it doesn't blow out the sensitivity.
   
2. Adjust the music volume so that it is at full, rather than being barely audible.
   
3. Fix the bug where you don't get an achievement for gathering all the hidden triangles.

If you want a quick fix, go to this download link[drive.google.com], make a backup of your data.win file in the GUNGODZ folder* (I recommend just renaming it "data_backup.win"), and replace it with the one I've provided. Boom. Dun.


*To get there quick if you've never done this before, right click on GUN GODZ in the steam library, select "Properties", then, in the window that pops up, go to the tab labeled "LOCAL FILES" and click "BROWSE LOCAL FILES...".

If you like getting your hands dirty (and want to know what I did), first you'll need to download the Undertale Mod Tool[github.com] from github.

Download it and unpack it on your desktop, then run it and open the "data.win" file in the GUNGODZ folder.

From here, the first change we'll make is for the "turning while shooting" and "shank" behaviors. Both of these issues are fixed by (navigating the sidebar) going to "Code" >> "gml_Object_Player_Step_0" and double clicking that entry. (You can use the search bar like in my picture below, if needed.)


From here, click on the "Decompiled" tab and scroll until you find the code below.


You'll need to double-click the code to edit it, but change it so that the code reads as it does below.


Notice that we deleted the lines reading "if (!mouse_check_button(1))" and "if (!keyboard_check(vk_space))". Navigate away from this tab to have it commit, and on to the next fix.

The second change is adjusting the music so that it's audible compared to the other sounds in the game. For some reason, the music was adjusted down to be just 1/5th the volume of all the other sounds. If you're like me and would prefer to hear this soundtrack clearly (and I think it's a selling point of the game), then navigate to "Code" >> "gml_Script_scrMusic" in the side pane and switch to decompiled view again.


The line "sound_volume(argument0, 0.2)" is the line we're looking at. That second argument, the "0.2" is what adjusts the music volume and can be any decimal between 0 and 1. I just set it to 1, but you can change this however you feel comfortable.


Now, the last issue, fixing the triangle/star achievement. On that side panel, navigate this time to "Code" >> "gml_Object_LevelSelect_Create_0" and navigate to the code chunk below.


For that "if (stars >..." statement, change it from "52" to "51, as below.


This needs to happen because there are only 52 stars/triangles in the game, and the "if---greater than" statement isn't triggered unless it is explicitly more than the number listed. So, if you get 52 triangles, that's still not greater than "52", so no achievement.

Anyhow, from here, navigate away from this tab (to make sure it commits the changes), then save your changes to the original file and you're done!

As I said in the acknowledgement section, thanks again to Ozymandias for their guide. You'll find some further comments at the end there that might be useful when it comes to configuration.

Enjoy your gunnin'!