All of these games works following an editor.(The Ones with RPG Maker category). Depending on the Maker used, the program to load the data and change is different, Player can open the game and mod it by himself changing lines and effects of items/values. In this case this one uses RPG Maker VX Ace. You need to downloaded a build(it's a paid program but well, this is internet after all), then with this build, there is a file in the folder u can use an RPG Maker Extractor(avaliable in some Forums like ULMF and F95), extract the data files, cg's, pictures, images... move those to the folder then open the game as if an project with the editor). Then do whatever u want, while using the "Test" option you can for example hold CTRL to walk throguh walls or in case of this game where the creator made a developer menu, hold right shift then press enter.
ALL RPG Maker base games can be edited. As long as use right extractor and right program to mod. When DLSite says RPG Maker MV, u need the virtual box extractor since it's their newest RPG Maker. The oldest(classic) is just RPG Maker, followed by VX, then Ace and lastly, the mentioned MV. Other than these there are also Wolf RPG Editor/Maker and another one that i forgot that creates games following same system as Fire Emblem(strategy focused).
Then we have Ren'py that can create visual novels...