I write through a translator. I'm Russian.
I have a few questions that I can't find the answers to. I will be glad of your help.

Adding graphics is not a problem, I learned that. Replacement is also not a problem. But I'm going to add new ones.
For example: the author made a new Power-Up, but it replaces another Power-Up. Is it possible to add a new one and still keep the old one?
NPC: I saw the authors make an NPC Pack, where there are 10 NPCs in 1 NPC at once. A good alternative is to save a lot of NPCs. Is it possible to add NPCs separately from each other and keep the original NPCs?
Also interested in adding new ones: levels, blocks, level backgrounds, music, etc.

I learned how to launch the world at once. I click on the file "world.wld" and run it through the program "smbx.exe ". The disadvantage is that then I can't choose: the number of players, choose a hero, screen mode, configure management and saving. I want to launch the game immediately with the game menu.
I used to see instructions somewhere on how to write "file.bat" to launch the game with different modes. Perhaps this is a workaround solution. But now I can't find this information.