The following was posted before I saw nova++'s post[/edit]
If you still want DEHACKED functionality, then you can actually still get it to run under DOSBox - with all the finicky DeHacked setup and ini tweaking.
More likely, if you still want to create DeHacked patches, then WhackEd might be more suitable. https://www.teamhellspawn.com/exl/whacked4/
If you want to modify the game, define your own monsters/weapons/other actors and so much more then you are starting to get into port-specific solutions that are unlikely to work in anything other than their intended port.
Our very own GZDoom has its own ZScript which is a very comprehensive programming language for altering many aspects of the game and the older DECORATE which can be simpler to use but is largely deprecated in favour of ZScript.
The 3DGE port has its own system which is also quite powerful, and ports such as Doomsday (and derivatives such as Risen3D) have definition files that can be modified. Other ports are likely to have their own systems too. I'm just not that familiar with them.
For the most part these days, DeHacked patches are not often used for much more than changing text (level names, end game messages etc) for maps that are targetted at cross port compatibility. Anything more advanced is usually handled by port-specific modifications.